MEDICAL 


hooper  foundation 
Accession 


/ 


ELEMENTS   OF 

MAMMALIAN  ANATOMY 


DAVISON 


MAMMALIAN  ANATOMY 

WITH   SPECIAL   REFERENCE   TO 

THE  CAT 

BY 

ALVIN    DAVISON,  PH.D. 

EX-FELLOW    OF    1'KINCBTON    UNIVERSITY;     PROFESSOR     OF    BIOLOGY   IN    LAFAYETTE    COLLEGE 


SECOND   EDITION,   REVISED 

WITH  114  ILLUSTRATIONS,  MOST  OF  WHICH  WERE  MADE 
BY  W.  H.  REESE,  A.M.,  FROM  THE  AUTHOR'S  DISSECTIONS 


' '  Study  nature,  not  books. ' ' 

— Agassi z. 


PHILADELPHIA 

P.    BLAKISTON'S   SON   &   CO 
1012  WALNUT  STREET 
1910 


COPYRIGHT,  1910,  BY  P.  BLAKISTON'S  SON  &  Co. 


PRESS  OF 

tyey  ERA  PRINTING  COMPAI* 
LANCASTER.  PA 


PREFACE  TO  THE  SECOND  EDITION. 


When  the  first  edition  of  this  book  was  published  less 
than  a  half  dozen  medical  schools  in  the  United  States 
required  the  entering  student  to  have  any  knowledge  of  the 
structure  of  the  lower  animals.  To-day  a  knowledge  of 
mammalian  anatomy  or  zoology  is  considered  one  of  the 
first  requisites  for  entering  upon  an  intelligent  study  of 
medicine.  The  signs  of  the  times  indicate  that  in  the  near 
future  no  medical  school  will  receive  students  without  some 
practical  knowledge  of  the  structure  of  a  mammal. 

That  the  students  of  modern  psychology,  the  teachers  of 
physiology  in  all  high  schools  and  the  directors  of  all 
gymnasiums  need  a  definite  knowledge  of  the  essentials  of 
the  anatomy  of  a  mammal,  is  becoming  more  and  more 
evident.  These  facts  and  the  steady  demand  for  the  first 
edition  of  this  book  have  been  the  principal  factors  in 
determining  the  preparation  of  a  second  edition. 

Owing  to  the  gradual  acceptance,  in  part  at  least,  of  the 
B.  N.  A.  nomenclature,  numerous  changes  have  been  made 
in  the  body  of  the  text.  The  names  used  in  this  edition  are 
such  as  have  found  favor  with  the  majority  of  American 
anatomists.  The  author's  easy  and  quick  method  of  prepar- 
ing the  skeleton  for  study  is  for  the  first  time  presented 
in  print.  In  several  instances  the  language  has  been  made 
more  clear,  and  several  new  figures  and  a  glossary  have 
been  added  which  will  be  of  special  help  to  the  beginning 
student  of  anatomy. 

ALVIN  DAVISON. 

11086 


PREFACE  TO  THE  FIRST  EDITION. 


Huxley  after  years  of  pedagogical  experience  reached 
the  conclusion  that  it  is  unwise  to  introduce  the  beginner 
at  once  to  new  and  strange  forms  of  microscopic  life  when 
it  is  possible  to  use  a  subject  of  which  the  student  is 
bound  to  know  something, — the  elementary  anatomy  of 
a  vertebrate  animal.  The  late  T.  Jeffrey  Parker  and 
numerous  other  eminent  zoologists  likewise  advocate  be- 
ginning zoological  work  by  studying  one  of  the  higher 
animals.  Since  the  majority  of  college  students  have  time 
for  only  one  year  of  zoological  work,  they  cannot  acquire 
a  fruitful  knowledge  of  both  vertebrates  and  invertebrates. 
A  study  of  the  former  enables  one  not  only  to  become 
familiar  with  the  anatomy  and  physiology  of  his  own  body, 
— a  matter  of  vital  importance, — but  throws  a  clear  light  on 
the  significant  problem  of  organic  evolution  such  as  is  not 
to  be  derived  from  a  study  of  invertebrate  forms.  Inas- 
much as  the  genealogical  histories  are  best  worked  out 
among  the  Mammalia,  and  since  a  careful  study  of  the 
anatomy  of  the  cat  familiarizes  one  with  the  anatomy  of 
the  human  body,  as  is  evidenced  by  the  fact  that  our  best 
medical  schools  now  advise  their  prospective  students  to 
dissect  either  a  dog,  a  cat,  or  a  rabbit  as  a  preparation  for 
their  later  work,  it  is  apparent  that  a  knowledge  of  the 
mammals  is  of  the  greatest  worth. 

This  brief  work  is  intended  to  acquaint  the  student  with 
the  general  structure  of  the  cat,  and  at  the  same  time  intro- 
duce him  to  some  of  the  most  important  morphologic 
features  of  the  Mammalia.  The  following  works  are  useful 
for  reference:  "Anatomical  Technology,"  Wilder  and 
Gage;  " Anatomy  of  the  Cat,"  Reighard  and  Jennings; 


vin  PREFACE    TO    THE    FIRST    EDITION 

"  Mammals  Living  and  Extinct,"  Flower  and  Leydekker; 
"  Primary  Factors  of  Organic  Evolution,"  E.  D.  Cope; 
"  Vertebrate  Zoology,"  J.  S.  Kingsley;  "  Anatomic  des 
Hundes,"  Ellenberger  and  Baum;  "Human  Physiology," 
Schenck  and  Giirber;  "  Osteology  of  the  Mammalia," 
Flower ;  "  Human  Histology,"  Piersol. 

In  the  preparation  of  this  book  I  have  consulted  a  large 
number  of  works  on  human  and  comparative  anatomy  and 
physiology.  Those  giving  most  assistance  are  the  works 
mentioned  above,  in  addition  to  "  Mammalian  Anatomy " 
by  Jayne,  "  Anatomic  Descriptive  et  Comparative "  by 
Strauss-Durckheim,  "  Nervose  Centralorgane  "  by  Edinger, 
and  "Vertebrate  Palaeontology"  by  Woodward.  I  am 
especially  indebted  to  my  artist,  Mr.  W.  H.  Reese,  of  the 
Phillipsburg  High  School,  for  the  care  and  patience  exer- 
cised in  making  the  drawings  from  my  own  dissections. 
Mr.  D.  S.  Hartline,  of  the  Bloomsburgh  State  Normal 
School,  has  read  the  entire  manuscript  and  made  valuable 
criticisms.  Above  all,  I  have  to  thank  Prof.  J.  S.  Kingsley 
for  numerous  valuable  suggestions  and  important  cor- 
rections in  the  manuscript. 

ALVIN  DAVISON. 


CONTENTS. 


PAGE. 

INTRODUCTION   I 

The  Biological   Sciences • I 

Classification  of  the  Animal  Kingdom 2 

Preparation  and   Preservation  of   Material 4 

GENERAL  STRUCTURE  OF  A  VERTEBRATE 13 

External  Features 18 

THE   SKELETON 21 

General  Terms  Used  in  Description  of  Bones 21 

Tabulation  of  Bones 22 

Structure  of  Bone 25 

Bones  of  the  Skull 26 

Vertebral   Column 41 

Sternum 48 

Ribs 50 

Thoracic   Limb 52 

Pelvic   Limb 64 

THE  JOINTS 73 

THE  MUSCLES 77 

ORGANS  OF  DIGESTION  105 

Alimentary  Canal 105 

Viscera    113 

Accessory  Glands  of  Digestion 121 

Peritoneum  , 124 

THE  VASCULAR  SYSTEM 129 

Heart   130 

Arteries  of  Trunk 132 

Arteries  of  Neck  and  Head 135 

Arteries  of  Thoracic  Limb 137 

Arteries   of    Pelvic   Limb 140 

Venous  System 142 

Lymphatic  System  149 

Ductless  Glands 154 

RESPIRATORY  SYSTEM  157 

EXCRETORY  AND  REPRODUCTIVE  SYSTEMS 164 

Glands  of  the  Skin 164 

Urinary  Organs    165 

Female  Organs  of  Reproduction 167 

Male  Organs  of  Reproduction 170 

ix 


x  CONTENTS. 

PAGE. 

NERVOUS  SYSTEM 175 

Brain    176 

External  Features 177 

Internal  Structure 180 

Spinal  Cord 193 

Fiber  Tracts  of  the  Central  Nervous  System 199 

Peripheral  Nerves 204 

Cranial  Nerves 205 

Spinal  Nerves 207 

Sympathetic   System 214 

Organs  of  Sense 218 

Cutaneous  219 

Olfactory 219 

Gustatory    220 

Visual  221 

Auditory 224 

GLOSSARY 23 1 

INDEX    243 


LIST  OF  ILLUSTRATIONS. 


FIG.  PAGE. 

1.  Specimen  Jar  4 

2.  Injecting  Syringe    5 

3.  Diagrammatic  View  of  Operation  for  Injection 6 

4.  Method  of  Making  Incision  in  the  Carotid  Artery  for  Injection  6 

5.  Method  of  Inserting  the  Cannula  into  a  Vessel 7 

6.  Palmar  Aspect  of  Cat's  Paw  with  Cannula  Inserted 8 

7.  Flat  Epithelium  Cells  from  the  Mouth 13 

8.  Involuntary  Muscle    13 

9.  Cells  of  Cartilage  14 

10.  Fibers  of  Voluntary  Muscle 15 

n.  Fibers  of  Connective  Tissue 16 

12.  Longitudinal  Section  of  the  Humerus  of  a  Kitten 23 

13.  Longitudinal  Section  of  the  Femur 24 

14.  Cross-section  of   Cat's  Femur 25 

15.  Diagram    of    the    Bones    of    the    Mammalian    Skull    Viewed 

Laterally   27 

16.  Dorsal  Aspect  of  the  Cat's  Skull 28 

17.  Ventral   Aspect  of   the    Skull   with   the    Left   Auditory   Bulla 

Removed  32 

18.  Cut  Surface  of  a  Sagittally  Bisected  Skull 35 

19.  Medial  or  Inner  Aspect  of  the  Mandible 38 

20.  Ventral  Aspect  of  Larynx,  Hyoid  Bones,  and  Tongue 39 

21.  Lateral  Aspect  of  the  Skeleton 42 

22.  Plan  of  a  Vertebra 44 

23.  Dorsocaudal  Aspect  of  Atlas 44 

24.  Lateral  Aspect  of  the  Axis 45 

25.  Latero-caudal  Aspect  of  a  Thoracic  Vertebra 45 

26.  Caudal  Aspect  of  Fourth  Lumbar  Vertebra 47 

27.  Dorsal  Aspect  of  the  Sacrum 47 

28.  Ventral  Aspect  of  the  Bones  of  the  Thorax 49 

29.  Caudal  Aspect  of  Sixth  Rib 50 

30.  Lateral  Aspect  of  the  Scapula 53 

31.  Caudal  Aspect  of  the  Clavicle 53 

32.  Cranial  Aspect   of   the   Humerus 54 

33.  Lateral  Aspect  of  the  Ulna 55 

34.  Medial  Aspect  of  the  Radius 56 

35.  Genealogy  of  the  Horse 57 

36A.  Dorsal  Aspect  of  Cat's  Manus 59 

xi 


x»  LIST   OF   ILLUSTRATIONS. 


36fi.  Generalized  Type  of   Carpus 59 

37.  Lateral  Aspect  of  Forelimb  of  Equus 60 

38.  Lateral  Aspect  of  Innominate  Bone 64 

39.  Ventral  Aspect  of  Innominate  Bones 64 

40.  Caudal  Aspect  of  Femur 66 

41.  Cranial  Aspect  of  Tibia 66 

42.  Medial  Aspect  of  Fibula 68 

43.  Dorsal  Aspect  of  Hind-foot 70 

44.  Diagram  of  a  Diarthrodial  Joint 73 

45.  Lateral  Aspect  of  Dissected  Knee-joint 74 

46.  Caudal  Aspect  of  Knee-joint 75 

47.  Ventral  Aspect  of  Trunk  and  Neck  Muscles 81 

48.  Lateral  Aspect  of  the  Muscles  of  the  Cat 88 

49.  Lateral  Aspect  of  the  Muscles  of  the  Thoracic  Limb 90 

50.  Medial  Aspect  of  the  Muscles  of  Thoracic  Limb 98 

51.  Ventral  Aspect  of  the  Muscles  of  Trunk  and  Thigh 101 

52.  Lateral  Aspect  of  the  Muscles  of  the  Leg 101 

53.  Caudal  Aspect  of  the  Muscles  of  Crus  and  Foot 102 

54.  Diagram  of  a  Gland 105 

55.  Diagram  of  the  Chief  Organs  of  the  Cat 106 

56.  Dorsal  Aspect  of  the  Tongue  and  Larynx 108 

.57.  Longitudinal  Section  of  the  Canine  Tooth 109 

58.  Lateral  Aspect  of  the  Permanent  Dentition no 

59.  Viscera  of  the  Human  Body 113 

60.  Ventral  Aspect  of  the  Alimentary  Canal 116 

61.  Transverse  Section  of  the  Cat 117 

62.  Cross-section  of  the  Cardiac  End  of  the  Stomach 117 

63.  Gastric  Glands  1 18 

64.  Cross-section  of  the  Small  Intestine 119 

65A.  Villi  and  Glands  of  Intestine 1 19 

65B.  Lacteals  and  Portal  System  of  Dog 120 

66.  Salivary  Glands  122 

67.  Diagram  of  the  Stomach  of  a  Ruminant 126 

68.  Photograph  of  the  Human'  Heart 130 

69.  Heart  Viewed  Ventrally 130 

70.  Heart  Viewed  Ventrally  with  Caudal  Third  Cut  off 131 

71.  Heart  Viewed  Dorsally 131 

72.  Chief  Arteries  of  the  Trunk 133 

73.  Ventral  Aspect  of  the  Arteries  of  the  Head  and  Neck 136 

74.  Arteries  of  the  Forelimb 138 

75.  Arteries  of  the  Leg 140 

76.  Cross-section  of  Artery  and  Vein 142 

77.  Vein  with  Valves 143 


LIST   OF   ILLUSTRATIONS.  xiu 


78.  Veins  of  Cat 145 

79A.  Arterial  System  of  a  Rabbit 147 

79B.  Arterial  System  of  a  Man 147 

80.  Ventral  Aspect  of  Chief  Lymphatic  Vessels  of  the  Cat 152 

81.  Photograph  of  the  Lymphatic  Capillaries  and  Vessels  of  Cat's 

Ear  153 

82.  Diagrammatic  Transverse  Section  of  the  Chest 158 

83.  Photograph  of  a  Lung  Corrosion  of  a  Puma 159 

84.  Termination  of  a  Bronchiole 161 

85.  Photograph  of  Human  Heart  and  Lungs 162 

86.  Ventral  Aspect  of  Female  Urogenital  System 165 

87.  Median  Longitudinal  Section  of  a  Kidney 166 

88.  Diagram  of  Structure  of  Kidney 166 

89.  Section  of  Ovary 169 

90.  Ventral  Aspect  of  Male  Reproductive  Organs 171 

91.  Spermatozoa   172 

92.  Dorsal  Aspect  of  the  Brain 177 

93.  Ventral  Aspect  of  the  Brain 179 

94.  Diagram  of  the  Ventricles 181 

95.  Sagittal  Section  of  the  Brain 183 

96.  Dorsal  Aspect  of  the  Brain  with  the  Cerebellum  and  Portion 

of  Cerebrum  Removed   185 

97.  Cross-section  of  the  Brain  Caudad  of  the  Optic  Chiasm 187 

98.  Cross-section  of  the  Brain  through  Anterior  Commissure 189 

99.  Photomicrograph  of  Cross-section  of  Human  Spinal  Cord. . . .  193 

loo.  Diagrammatic  Section  of  Spinal  Cord 195 

IOT.  Nerve-cell    196 

102.  Diagram  of  the  Relation  of  Cells  and  Fibers  in  the  Spinal  Cord  197 

103.  Diagram  of  Some  Fiber-tracts 200 

104.  Diagram  of  Chief  Fiber-tracts  of  the  Mammalian  Brain 202 

105.  Ventral  Aspect  of  the  Branchial  Plexus 208 

106.  Ventral  Aspect  of  the  Nerves  of  the  Pelvic  Limb 212 

107.  Cranial  Half  of  Sympathetic  System 215 

108.  Caudal  Half  of  Sympathetic  System 217 

109.  Pacinian  Corpuscle 219 

1 10.  Longitudinal  Section  of  the  Eye 222 

in.  Diagram  of  the  Mammalian  Ear 225 

112.  Section  of  the  Cochlea  of  the  Calf 226 

1 13.  Photograph  of  Human  Brain 227 

1 14.  Brain  of  the  Rabbit 229 


ELEMENTS 

OF 


MAMMALIAN  ANATOMY. 


ERRATA 

Page  33>  9th  line  from  bottom,  for  "  Fig.  90"  read 
"Fig.  93." 

Page  54,  3d  line  from  bottom,  for  "Figs.  72  and  89  " 
read  "  Figs.  74  and  105." 

Page  77,  loth  line  from  top,  for  "  Fig.  91  "  read  "  Figs. 
107  and  ic8." 

Page  78,  1 6th  line  from  top,  for  "  abductor  muscles" 
read  ' '  adductor  muscles. ' ' 

Page  78,  1 7th  line  from  top,  for  "abductor"  read 
"adductor." 

Page  78,  i8th  line  from  top,  for  "abductors"  read 
"  adductors." 

Page  7  ,  2d  line  from  bottom,  for  "Fig.  47  "  read 
"Fig.  48." 

Page  175,  1 2th  line  from  top,  for  "  Figs.  94  and  95  " 
read  "  Figs.  107  and  108." 


ot  the  world,     me  lion  ana  tiger  are  touna  wild  only  m 

2  I 


ELEMENTS 

OF 


MAMMALIAN  ANATOMY. 


INTRODUCTION. 

Since  this  book  is  designed  for  the  use  not  only  of 
students  who  have  pursued  the  study  of  biology  for  some 
time,  but  also  for  those  making  their  first  actual  acquaint- 
ance with  the  subject,  it  may  be  well  to  call  attention  to 
the  fact  that  any  animal  or  plant  may  be  considered  from 
several  different  standpoints.  A  general  study  of  structure 
and  of  the  relations  of  the  various  systems  and  organs  is 
known  as  Anatomy.  Histology  concerns  itself  with  the 
cell  and  cell  aggregates  or  tissues  composing  the  organs. 
These  two  sciences  are  included  in  Morphology,  a  term 
which  by  many  is  made  to  include  also  Embryology  or 
Ontogeny,  treating  of  the  development  of  an  organism  from 
the  egg,  or  its  vegetable  homologue,  to  the  period  of  assum- 
ing adult  characteristics.  Since  ontogeny  deals  not  only 
with  the  growth  of  structure  but  also  the  process  of  growth, 
it  may  likewise  be  included  under  Physiology,  a  science 
which  has  for  its  province  the  investigation  of  the  functions 
of  the  organs  and  systems.  A  special  field  of  physiology 
having  for  its  consideration  the  operations,  especially  the 
conscious  operations  of  the  nervous  system,  constitutes  the 
science  of  Psychology. 

The  same  species  of  animals  are  not  found  in  all  parts 
of  the  world.  The  lion  and  tiger  are  found  wild  only  in 


2  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

the  old  world,  while  the  opossum  is  confined  to  the  new 
world.  Again,  many  species  of  animals  whose  fossil  re- 
mains indicate  their  existence  on  earth  several  millions  of 
years  ago,  have  at  present  no  living  representatives.  A 
consideration  of  this  geographical  and  stratigraphical  loca- 
tion of  organisms  forms  the  science  of  Distribution.  The 
science  of  Phytogeny  seeks  to  discover  the  geological 
ancestral  history  of  an  organism. 

A  casual  glance  shows  at  once  striking  similarities  and 
differences  between  the  common  cat,  the  lion,  and  the  tiger. 
All  have  retractile  claws,  the  same  number  and  kind  of 
teeth,  and  the  same  number  of  toes.  On  the  other  hand, 
the  resemblances  between  these  cat-like  animals  and  the 
dogs  are  less  marked,  while  the  differences  are  more  strik- 
ing. The  cats  and  dogs  resemble  each  other  more  closely 
than  either  does  a  horse.  Horses,  dogs,  and  cats  have 
numerous  characters  in  common  which  are  not  present  in 
birds.  The  recognition  of  such  resemblances  and  differ- 
ences furnishes  a  basis  of  classification,  the  treatment  of 
which  forms  the  science  of  Taxonomy. 

The  following  is  a  brief  classification  of  the  animal 
kingdom : 

Invertebrata :     Animals  with  no  skeletal  axis  and  without  a  central 
nervous  system  entirely  dorsal  of  the  alimentary  canal. 
Protochordata:  Small  marine  forms  having,  during  part  of  their  life 
at  least,  a  rudimentary  skeletal  axis  and  other  fea- 
tures marking  them  as  a  connecting-link  between  the 
invertebrates     and     vertebrates.       Tunicates     or     sea 
squirts,  Amphioxus. 
Vertebrata:         Forms    with    a    skeletal    axis    and    dorsal    nerve-cord 

whose  anterior  end  is  dilated  into  a  brain. 
PISCES  (fish). 

AMPHIBIA  (frogs,  toads,  and  salamanders). 
REPTILIA  (snakes  and  lizards). 
AVES    (birds). 


INTRODUCTION.  3 

MAMMALIA   (vertebrates  suckling  their  young). 

Prototheria:  Oviparous  mammals.  Ornithorhynchus. 
or  duck-bill  and  Echidna  or  spiny 
ant-eater. 

Eutheria:  Viviparous  mammals  with  anus  and 
urogenital  opening  distinct. 

Marsupialia  (opossums  and  kangaroos). 

Insectivora  (moles,  shrews,  and  hedge- 
hogs). 

Edentata  (sloths  and  ant-eaters). 

Chiroptera  (bats  and  flying  foxes). 

Rodentia  (rabbits,  squirrels,  mice,  and 
rats). 

Cetacea    (whales,   porpoises,    and   dol- 
phins). 

Sirenia  (sea  cow). 

Ungulata    (the  hoofed  mammals). 

Carnivora     (dogs,    cats,    wolves,    and 
foxes). 

Primates    (monkeys  and  man). 

A  glance  at  the  above  outline  shows  that  the  class  Mam- 
malia is  divided  into  two  subclasses,  the  latter  of  which 
includes  ten  orders.  Each  of  these  orders  consists  of 
several  families  which  in  turn  are  composed  of  genera  made 
up  of  species.  The  order  Carnivora  includes  eleven  fami- 
lies, of  which  Canidae  (the  dogs),  Felidae  (the  cats),  and 
Ursidse  (the  bears)  are  the  most  frequently  seen  in  America. 
The  family  Felidae  is  represented  by  only  two  living  genera, 
Cyncelurus  and  Felis.  The  genus  Felis  includes  several 
species,  of  which  Felis  leo  (the  lion),  Felis  tigris  (the 
tiger),  and  Felis  domestica  (the  cat)  are  the  most  familiar. 
Of  the  last  species,  there  are  several  varieties,  such  as 
Maltese,  Angora,  and  Manx  cats. 

Linnaeus,  born  in  Sweden,  1702,  invented  the  system  of 
binomial  nomenclature  in  accordance  with  which  the  scien- 
tific name  of  every  plant  and  animal  is  composed  of  two 
parts,  the  generic  and  specific.  Thus  the  house  cat  is 
designated  Felis  domestica;  the  lion,  Felis  leo;  the  dog, 


4  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

Canis  familiaris;  the  wolf,  Cams  lupus;  the  pig,  Sus  scrofa; 
the  red  deer,  Cervas  elephas;  the  elephant,  Elephas 
Africamts;  the  ourang-outang,  Simla  satyrus;  and  man, 
Homo  sapiens. 

METHODS  OF  PRESERVING  MATERIAL. 

Alcohol  has  been  widely  used  as  a  preservative,  but  owing 
to  the  fact  that  it  is  expensive  and  quickly  evaporates  from 
the  specimen  exposed  to  the  air,  thereby  rendering  the  parts 
dry  and  brittle,  its  use  has  been  largely 
supplanted  by  formalin.    Formalin,  CH2O, 
is  often  sold  under  the  names  of  formose, 
formol,  formine,  formalosa,  and  formal- 
dehyd.     It  can  be  purchased   for  about 
thirty  cents  a  pound.     For  preserving  any 
animal   or  plant,   the  concentrated  40% 

formaldehyd  is  diluted  with  water  in  the 
FIG.  i.  SPECIMEN  .  -  r  «•  .1  •  «  j 

JAR-  proportion  of  ninety-five  parts  of  the  lat- 

ter to  five  parts  of  the  former.  It  is 
evident,  therefore,  that  one  pound  of  formaldehyd  will  make 
about  ten  liters  of  preserving  fluid. 

The  specimens  may  be  kept  a  year  or  two  without  chang- 
ing the  formalin  in  ordinary  stone  jars  with  covers,  but 
for  permanent  preservation  the  glass  jar  with  the  ground- 
glass  cover  should  be  used  (Fig.  i). 

Preparation  of  Vascular  System. — To  render  the  vessels 
plainly  visible  and  distinguish  the  arteries  from  the  veins, 
it  is  advisable  to  inject  the  former  with  a  red  mass  and  the 
latter  with  a  blue  mass.  These  fluid  masses  should  be  of 
such  a  character  as  to  harden  in  a  short  time  after  injection, 
so  that  they  will  not  run  out  when  the  vessels  are  cut  during 
dissection. 

A  syringe  of  hard  rubber,  having  a  capacity  of  about  two 


INTRODUCTION. 


ounces,  serves  very  well  for  injection.  A  cannula  of 
correct  size  may  be  had  by  asking  the  druggist  for  the 
filling  cannula  of  the  Parke  Davis  serum 
syringe.  The  end  to  be  inserted  into 
the  blood-vessel  should  be  ground  off 
obliquely  and  smoothly  on  a  whetstone. 
The  connection  between  the  cannula  and 
nozzle  is  formed  by  stiff  rubber  tubing 
which  should  be  securely  tied  to  the  can- 
nula (Fig.  2). 

The  injecting  mass  is  prepared  by 
thoroughly  mixing  100  c.c.  of  water,  20 
c.c.  of  glycerin,  20  c.c.  of  concentrated 
formalin,  and  85  gm.  of  common  laun- 
dry starch.  One-half  should  be  colored 
red  by  adding  to  it  one  or  two  grams  of 
powdered  carmin  made  into  a  paste  with 
a  few  drops  of  ammonia,  and  the  other 
colored  blue  by  dissolving  in  it  a  gram 
or  two  of  soluble  Berlin  blue.  These 
liquid  masses,  after  being  passed  through 
a  fine  wire  strainer  or  a  coarse  piece  of 
cheese-cloth  stretched  across  a  funnel, 
may  be  preserved  for  any  length  of  time 
in  covered  jars. 

The  animal  may  be  anesthetized  by 
placing  it  in  a  tight  box  with  a  cloth  or 
absorbent  cotton  wet  with  30  c.c.  of 
ether  or  chloroform.  If  only  the  ar- 
teries are  to  be  injected,  the  cat  may 
remain  in  the  box  until  dead;  but  if  the 
veins  are  also  to  be  injected,  it  is  preferable  to  use  ether  for 
the  anesthetic  and  then  remove  the  animal  to  the  tray  as 
soon  as  it  is  unconscious,  and  reflect  a  portion  of  skin,  ex- 


FIG.  2.  INJECTING 
SYRINGE.  X  &. 

p,  Plunger  handle ; 
b,  barrel;  pi, 
nozzle ;  c,  can- 
nula ;  r,  rubber 
tube ;  dt,  point 
of  detachment ; 
s,  string. 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


posing   the   external   jugular   veins    (Fig.    3).     With   the 

curved  forceps  thrust  beneath  the  vein  a  cord  may  be  pulled 

through  and  tied  in  a  loose 
knot.  One-half  inch  from 
the  latter  a  second  cord 
should  be  tied  around  the 
vein  loosely.  An  oblique 
cut  (Fig.  4)  with  the  point 
of  the  scissors  directed  cau- 
dad  is  then  made  in  the  veins 
between  the  cords.  The  in- 
cision should  extend  about 
half-way  through  the  vessel. 
Absorbing  the  blood  with 
absorbent  cotton  as  it  runs 
from  the  vessel  will  prevent 
clogging.  I  f  too  much  ether 
has  not  been  used,  the  blood 
will  continue  running  fifteen 
minutes.  When  it  has  nearly 
ceased  flowing,  the  carotid 
artery  must  be  found  by 

making  a  slit  in  the  muscle  alongside  of  the  trachea  just 

mediad  of  the  jugular,  as  indicated  by  the  line  d  (Fig.  3). 

Having  cut  through  the  muscle, 

two  white  cords  are  seen  along 

either     side    of    the    trachea. 

The  medial  one  may  be  red,  as 

it  is  the  carotid  artery.     The 

lateral  one,  lying  in  the  same 

sheath   with  the  preceding,   is 

the    vagus    or    tenth    cranial 

nerve.      Separate     the     artery 

from  the  nerve  and  tie  two  cords  loosely  around  the  ves- 


FIG.  3.  DIAGRAMMATIC  VIEW  OF 
OPERATION  FOR  INJECTION. 

d,  Broken  line  showing  course  of 
the  carotid  artery  beneath;  b, 
string  loosely  tied ;  c,  transverse 
vein  uniting  external  jugulars; 
a,  points  of  curved  forceps  con- 
taining string. 


FIG.  4.  METHOD  OF  MAKING 
INCISION  IN  THE  CAROTID 
ARTERY  FOR  INJECTION. 


INTRODUCTION. 


sel  as  in  the  case  of  the  jugular.  Lift  up  the  artery  with 
the  index  finger  (Fig.  4),  and  make  an  oblique  incision 
with  the  scissors.  The  cannula  with  the  connecting  tube 
attached  should  then  be  inserted  caudad  in  the  oblique  cut 
of  the  artery  (Fig.  5),  and  the  string 
s  drawn  tight  so  as  to  hold  the  cannula 
in  place.  The  string  st  should  then 
be  tightened  to  prevent  the  injection 
mass  from  running  out  where  the  can- 
nula is  inserted.  After  stirring  the 
red  mass,  filling  the  syringe,  and  slip- 
ping the  nozzle  into  the  connecting 
tube  the  operator  should  press  slowly 
but  continuously  on  the  plunger  until 
that  portion  of  the  carotid  craniad  of 
the  string  st  is  well  distended.  In  a 
large  cat  this  will  not  occur  until  the 
syringe  is  nearly  or  quite  empty. 
When  the  vessels  are  full,  the  can- 
nula is  withdrawn  while  the  string  ^  is 
tightened.  The  syringe  is  washed  out,  after  which  the  blue 
mass  is  well  stirred  and  injected  caudad  into  the  external 
jugular  in  the  same  manner  as  described  for  the  arteries. 

By  making  a  slit  about  three  inches  long  in  the  abdominal 
wall,  a  fold  of  the  intestine  may  be  pulled  out  so  that  its 
lumen  can  be  filled  with  about  200  c.c.  of  15%  formalin. 
The  same  amount  should  be  injected  into  the  lungs  by 
inserting  the  cannula  caudad  into  the  ventral  wall  of  the 
trachea.  If  the  cat  is  not  to  be  used  at  once,  it  may  be 
preserved  indefinitely  in  a  jar  of  five  per  cent,  formaline. 

The  portal  system  is  not  injected  through  the  jugular 
vein.  The  portal  trunk  just  caudad  of  where  it  enters  the 
liver  may  be  found  by  cutting  a  piece  from  the  abdominal 
wall  on  the  right  ventral  aspect  just  caudad  of  the  last  rib. 


FIG.  5.  METHOD  OF 
INSERTING  THE  CAN- 
NULA INTO  A  VES- 
SEL. 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 

After  two  loose  knots  are  tied  around  this  trunk  as  directed 
for  the  jugular,  the  cut  is  made  and  the  cannula  inserted 
caudad.  About  15  c.c.  of  the  blue  mass  may  be  injected 
into  the  portal  system  of  a  large  specimen.  This  should 
not  be  injected  until  the  other  systems  have  been  filled. 

The  lymphatic  system  must   likewise  be   injected   for 
demonstration.     While  the  cat  is  being  anesthetized,  5  gm. 
of  soluble  Berlin  blue  are  dissolved  in  100  gm.  of  water, 
and   the  solution   warmed   to   about   the 
temperature   of   the   body.     As   soon   as 
the  cat  is  unconscious  the  syringe  should 
be  warmed  by  filling  it  with  hot  water, 
and  the  point  of  the  cannula  pushed  ob- 
liquely proximad  under  the  thick  skin  on 
the  palm    (Fig.    6)    of   the  paw.      The 
syringe  after  being  half  filled  with  Berlin 
FIG.    6.     PALMAR     klue  solution  is  attached  to  the  cannula 

ASPECT  OF  CAT'S      and   the  plunger  pushed   in   very   slowly 
PAW  WITH  CAN-  -  .         .       .    .  / 

NULA  INSERTED.  t.  so  tnat  one- fourth  of  the  amount  in  the 

syringe  is  forced  out  in  ten  minutes. 
While  the  injection  is  being  made  the  limb  should  be  gently 
massaged  by  pinching  and  rubbing  from  the  foot  toward 
the  body.  This  facilitates  the  flow  of  the  liquid  in  the 
lymph-vessels.  In  this  manner  the  lymphatics  of  each  limb 
are  filled.  The  author  has  been  able  to  fill  the  left  thoracic 
duct  by  continuing  the  injection  for  about  twenty  minutes 
in  the  palm  of  the  left  paw.  The  lymphatics  of  the  head 
and  neck  may  be  injected  in  a  similar  manner  by  inserting 
the  cannula  beneath  the  skin  on  the  tip  of  the  ear,  the  tip 
of  the  tongue,  the  tip  of  the  nose,  and  the  lips. 

In  order  to  inject  the  lacteals  the  abdominal  cavity  must 
be  opened,  and  the  cannula  inserted  very  obliquely  into  the 
wall  of  the  small  intestine  so  that  its  point  is  between  the 
mucous  and  muscular  coats.  The  half -filled  syringe  being 


INTRODUCTION.  9 

attached,  very  gentle  pressure  should  then  be  exerted  on  the 
plunger,  until  the  blue  solution  appears  in  the  lacteals.  To 
inject  all  the  lacteals  it  is  necessary  to  insert  the  cannula  into 
the  wall  of  the  intestine  at  a  dozen  different  places.  To  fill 
the  thoracic  duct,  injection  may  be  made  into  the  large 
lymphatic  gland  lying  at  the  point  where  the  converging 
blood-vessels  of  the  mesentery  meet.  The  best  solution  for 
injecting  the  thoracic  duct  is  made  by  dissolving  7  gm.  of 
gelatin  in  a  warm  Berlin  blue  solution  (4  gm.  of  Berlin 
blue  to  100  c.c.  water).  This  should  be  filtered  through  a 
single  layer  of  absorbent  cotton  and  then  injected  while  still 
quite  warm.  In  all  cases  injections  to  fill  the  lymphatics 
must  be  warm  and  must  be  pushed  in  very  slowly.  These 
lymphatic  injections  are  best  preserved  by  injecting  the 
trachea  and  intestine  with  95%  alcohol  and  immersing  the 
cat  in  a  jar  of  70%  alcohol. 

Preparation  of  a  Mammal  for  Dissection  of  the 
Muscles,  Peripheral  Nerves  and  Viscera. — The  simplest 
method  is  to  anesthetize  the  animal  as  before  described  and 
then  remove  the  skin,  taking  great  care  to  avoid  cutting 
away  the  superficial  muscles.  The  cannula  should  be 
pushed  through  into  the  trachea  and  100  c.c.  of  15%  for- 
maline injected  to  fill  the  lungs.  An  equal  amount  of 
formaline  should  be  injected  into  the  stomach  through  a 
glass  tube  pushed  down  the  esophagus.  The  same  quantity 
of  formalin  should  be  injected  at  two  or  three  different 
places  into  the  intestines  by  making  a  median  incision  into 
the  abdominal  wall  and  pulling  out  a  loop  of  the  intestine 
into  which  the  cannula  may  be  thrust.  The  specimen  is 
then  to  be  immersed  in  a  jar  of  5%  formalin.  A  better 
method  is  to  inject  into  the  carotid  artery  200  c.c.  of  glyceri- 
nated  formalin  (water  140  c.c.,  glycerin  30  c.c.,  formalin 
30  c.c.),  and  half  that  amount  into  the  intestine  and  trachea. 
The  specimen  may  then  be  preserved  in  5  %  formalin. 


io  ELEMENTS   OF   MAMMALIAN   ANATOMY.. 

Preparation  of  the  Central  Nervous   System. — The 

animal  may  be  killed  either  with  chloroform  or  ether. 
About  200  c.c.  of  formal-bichromate  (170  c.c.  of  5% 
potassium  bichromate  and  30  c.c.  of  formalin)  are  then 
injected  slowly  craniad  into  the  carotid  artery  (Figs.  3,  4, 
and  5).  After  skinning,  the  eyes  should  be  cut  out  and  the 
flesh  removed  from  the  head  and  dorsal  side  of  the  vertebral 
column.  On  a  line  connecting  the  caudal  borders  of  the 
orbits,  cut  through  the  skull  to  the  brain  with  the  bone 
cutters  and  remove  piece  by  piece  the  roof  of  the  skull. 
Next  cut  away  the  lateral  walls  down  to  the  base  of  the 
brain.  Care  must  be  exercised  in  laying  bare  the  cere- 
bellum, and  cutting  loose  the  tertorium  cercbelli,  the  plate 
of  bone  separating  the  cerebrum  from  the  cerebellum.  The 
spinal  cord  is  next  laid  bare  dorsally,  beginning  with  the 
atlas,  by  cutting  through  the  pedicles  of  the  neural  arches 
on  either  side.  With  a  sharp  knife  or  a  pair  of  scissors 
the  spinal  nerves  may  then  be  cut  and  the  cord  lifted  from 
behind  forward  out  of  its  bed,  until  the  brain  is  reached. 
The  latter  must  be  carefully  raised  while  the  nerves  at  its 
base  are  cut,  and  the  dura  mater  loosened. 

The  brain  is  firm  enough  to  dissect  as  soon  as  removed, 
but  it  is  better  to  further  harden  it  and  differentiate  the 
white  and  gray  matter  by  placing  it  in  weak  formal-bichro- 
mate (5%  formalin,  500  c.c.  +  5%  potassium  bichromate, 
500  c.c.)  one  week  in  the  dark.  Light  causes  a  precipitate. 
At  the  end  of  one  week  the  specimen  should  be  placed  in 
1000  c.c.  of  5%  formalin  for  another  week,  after  which  it 
is  ready  for  dissection.  In  case  brains  of  calves  or  sheep 
are  used  a  hammer  and  bone  chisel  are  necessary  for  open- 
ing the  skull.  The  head  should  first  be  nailed  to  the  tray. 
As  soon  as  the  brain  is  removed  it  should  be  placed  in  a 
large  pan  of  water  and  the  dura  mater  carefully  cut  away, 
the  clotted  blood  washed  off  and  a  syringeful  of  strong 


INTRODUCTION.  n 

formal-bichromate  injected  into  the  third  ventricle  by  push- 
ing the  cannula  about  half  an  inch  through  the  infun- 
dibulum  (Fig.  90).  The  brain  of  a  sheep  or  calf  will  be 
very  soft  when  removed,  as  it  cannot  be  hardened  pre- 
viously by  injecting  the  hardening  fluid  into  the  arteries. 
Therefore  it  is  necessary  to  lay  the  specimen  on  absorbent 
cotton  in  the  jar  of  formal-bichromate,  which  must  be 
exchanged  for  fresh  fluid  on  the  second  and  third  days. 
At  least  two  weeks  are  required  for  hardening  the  brain  of 
a  sheep  or  calf,  after  which  it  is  placed  in  5%  formalin 
for  a  week  or  more  to  wash  out  the  bichromate  before 
dissection.  Brains  are  best  preserved  permanently  in  85% 
alcohol. 

Preparation  of  the  Osseous  System. — A  mounted  skele- 
ton of  the  cat  may  be  purchased  for  about  eight  dollars.  It 
is  far  more  satisfactory,  however,  to  use  the  disarticulated 
bones  for  study.  These  are  easily  prepared  in  the  follow- 
ing manner :  As  soon  as  the  animal  is  dead,  the  skin  and  the 
greater  part  of  the  flesh  should  be  cut  away  and  the  internal 
organs  removed.  The  bones  with  much  flesh  remaining  on 
them  are  then  put  into  7000  c.c.  of  water  containing  150 
grams  of  gold  dust  This  may  then  be  boiled  from  two  to 
four  hours  but  better  results  are  given  by  using  the  low 
flame  and  keeping  the  solution  at  a  temperature  between 
75  and  90  degrees  centigrade  from  3  to  6  hours.  As  soon 
as  the  flesh  falls  freely  off  the  bones  they  should  be  brushed 
clean  in  a  pan  of  water  and  the  brain  broken  to  pieces  with 
a  bent  wire  thrust  into  the  foramen  magnum.  The  con- 
tents of  the  skull  may  then  be  washed  out  under  the  tap. 
This  treatment  renders  the  bones  perfectly  clean,  white  and 
free  from  grease. 

By  heating  the  bones  from  one  to  two  hours  only  and 
not  allowing  the  temperature  to  rise  above  85  degrees,  the 
flesh  may  be  brushed  from  the  limbs  without  removing  the 


12  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

ligaments  holding  the  bones  together.  When  dry,  the  bones 
are  held  firmly  in  their  natural  relations.  In  treating  the 
skeletons  of  kittens  or  those  of  smaller  animals  such  as 
mice,  birds  and  frogs,  only  one  half  the  amount  of  gold 
dust  should  be  used  and  a  temperature  between  70  and  80 
degrees  maintained. 


GENERAL  STRUCTURE. 

The  study  of  any  vertebrate  reveals  the  presence  of 
numerous  organs,  each  of  which  is  for  the  performance 
of  a  particular  function.  Thus  the  heart  is  the  organ  for 
the  propulsion  of  the  blood,  the  kidney  for  the  elimination 
of  the  nitrogenous  waste.  Several  organs  combined  for  a 
common  purpose  constitute  a  system.  The  heart,  with  the 
various  vessels  for  conveying  the  blood,  forms  the  circula- 
tory system.  The  following  eight  systems  are  found  in  all 


FIG.  7.     FLAT  EPITHELIUM  CELLS        FIG.  8.     INVOLUNTARY  MUSCLE- 
FROM  THE  MOUTH.    X  150.  CELLS.     X  250. 

n,  Nucleus  of  the  cell.  n,  Nucleus  of  a  cell. 

Mammalia:  Osseous  or  bony,  muscular,  digestive,  respira- 
tory, vascular,  excretory,  reproductive,  and  nervous. 

The  relative  locations  of  the  various  systems  are  repre- 
sented diagrammatically  in  Fig.  54.  The  organs  have  the 
same  arrangement  throughout  all  the  orders  of  mammals. 
Moreover,  the  minute  structure  of  the  same  organ  is  so 
similar  in  the  different  species  that  in  many  cases  even  the 
microscope  will  not  enable  one  to  tell  from  which  of  several 
kinds  of  mammals  the  organ  has  been  taken.  The  organs 
are  composed  of  four  classes  of  tissues :  Epithelial,  which 
covers  all  free  surfaces;  connective,  forming  the  bones, 
binding  together  the  muscular  fibers  and  elements  of  the 

13 


1 4  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

nervous   system   and   making  up  cartilage   and   ligaments 

(Fig.    n);  muscular,  composing  the  greater  part  of  the 

muscular  system;  and  nervous,  constitut- 

•  .    '  ing  the  nervous  system  (Fig.  97). 

,  • 

;:^;  The  naked  eye  is  unable  to  distinguish 

the  elements  of  the  tissues,  but  the  micro- 
scope reveals  the  fact  that  each  kind  of 
FIG.  9.  CELLS  OF  tissue  is  formed  of  either  cells  or  fibers 

iC5oRTILAGE'  or>  as  is  most  frequently  the  case,  a  com- 

bination of  both. 

The  different  relative  arrangements  of  these  anatomic 
elements,  together  with  their  morphology,  permit  one  to 
know  from  what  organ  any  particular  section  of  tissue 
under  consideration  has  been  taken. 

These  ultimate  units  of  structure  are  still  further  resolved 
into  parts  by  the  chemist,  who  has  shown  that  they  are 
composed  largely  of  carbon,  hydrogen,  oxygen,  and  nitro- 
gen. Since  there  can  be  no  energy  developed  in  the  body 
without  the  disintegration  and  consequent  death  of  some  of 
the  particles  composing  the  millions  of  tiny  cells,  it  is  plain 
that  they  must  have  their  losses  replaced  in  order  to  con- 
tinue their  existence.  Therefore  a  method  of  preparing  the 
food  for  the  use  of  the  cells,  and  a  way  of  transporting  it 
to  each  of  them  are  necessary. 

The  former  is  accomplished  by  the  digestive  system, 
which,  through  the  agency  of  the  salivary,  gastric,  pan- 
creatic, and  other  glands,  transforms  the  food  into  a  special 
liquid  state  capable  of  being  absorbed  by  the  millions  of 
minute  finger-like  villi  of  the  small  intestine  (Fig.  63). 
Thence  it  is  transferred  by  the  lacteal  vessels  and  veins  to 
the  heart,  whence  it  is  conveyed  by  the  arteries  to  their 
capillary  distribution  in  the  neighborhood  of  every  cell  in 
the  body. 

The  dead  matter  or  waste  material  resulting  from  the 


GENERAL  STRUCTURE.  15 

cell  activity  is  of  two  kinds,  gaseous  and  liquid.     Both 
diffuse  through  the  capillary  walls  into  the  blood.     The 


FIG.  10.     PHOTOMICROGRAPH  OF  FIBERS  OF  VOLUNTARY  MUSCLE.     X  100. 
Note  the  finer  threads  of  connective  tissue. 

former,  which  is  carbon  dioxid,  is  carried  to  the  heart  and 
thence  by  the  pulmonary  arteries  to  the  lungs,  where  it 
passes  into  the  terminal  branches  of  the  trachea,  and  finally 
by  expiration  reaches  the  exterior.  The  liquid  excretion  is 
transported  by  means  of  the  veins  and  arteries  to  the 
kidneys,  where  it  diffuses  through  the  walls  of  the  capil- 
laries into  the  minute  tubules  opening  into  the  ureters  lead- 
ing to  the  bladder.  It  must  be  remembered  that  the 


1 6  ELEMENTS    OF   MAMMALIAN    ANATOMY. 

material  known  as  feces  passed  out  of  the  alimentary  canal 
through  the  anus  is  not  an  excretion  of  the  cells  of  the  body, 
but  largely  that  portion  of  the  food  not  transformed  into  a 
condition  permitting  it  to  be  absorbed  by  the  villi. 


FIG.  ii.    FIBERS  OF  CONNECTIVE  TISSUE.      X  300. 

In  addition  to  these  systems  necessary  for  the  mainten- 
ance of  life,  the  cat  requires  a  means  for  supporting  the 
body  and  moving  about,  furnished  by  the  osseous  and 
muscular  systems.  The  osseous  system  serves  not  only  for 
support  and  locomotion,  but  also  for  the  protection  of  the 
delicate  vital  organs.  The  skull  and  spinal  column  contain 
the  brain  and  spinal  cord,  while  the  heart  and  lungs  are 
well  shielded  by  the  dorsal  vertebrae,  the  ribs,  and  sternum. 
Likewise  the  muscles  ward  off  serious  injuries  from  the 
blood-vessels,  as  they  cover  to  a  considerable  depth  nearly 


GENERAL   STRUCTURE.  17 

all  large  arteries,  and  also  aid  by  their  contraction  in  moving 
the  lymph  through  the  numerous  lymphatic  vessels  extend- 
ing from  the  extremities  to  the  jugular  veins. 

These  systems  previously  described  are  capable  of  per- 
forming their  functions  only  when  supplied  with  nerves 
through  which  impulses  can  be  transmitted  from  the  brain 
and  spinal  cord.  Stimuli  sent  by  the  brain  or  cord  through 
the  nerves  cause  the  gastric  juice  to  flow  into  the  stomach, 
the  bile  and  pancreatic  secretions  to  be  formed  and  poured 
forth  into  the  intestines,  the  kidneys  to  eliminate  the  waste 
from  the  blood,  the  heart  to  beat,  and  the  muscles  to  contract 
and  relax. 

The  only  system  which  is  not  absolutely  necessary  to  the 
life  of  the  cat  is  the  reproductive;  but  this  is  required  for 
the  continuance  of  the  species.  It  is  not,  however,  func- 
tional during  the  entire  life,  but  as  a  rule  only  from  the 
end  of  the  first  to  the  tenth  year. 

PRACTICAL   QUESTIONS   AND   SUGGESTIONS. 

1.  What   advantages   are   derived   from   the   study   of   mammalian 
anatomy? 

2.  Define  morphology  and  state  a  fact  from  that  science. 

3.  What  two  sciences  does  biology  include? 

4.  What  five  sciences  are  included  in  zoology? 

5.  Make  a  physiologic  statement  concerning  the  heart. 

6.  State  five  facts  belonging  to  the  science  of  distribution. 

7.  What  is  taxonomy? 

8.  Name  five  classes  of  vertebrates. 

9.  By  examining  specimens  discover  what  external  feature  distin- 
guishes a  reptile  from  an  amphibian. 

10.  Do  all   mammals  have   hair? 

n.  What  habit  is  common  to  no  other  vertebrates  except  mammals? 

12.  Give   two   points   of   difference   between   the   two   subclasses   of 
Mammalia. 

13.  Name  the  ten  orders  of  Eutheria  and  give  an  example  of  each. 

14.  Which  orders  derive  their  names  from  the  habits  of  the  animals? 

15.  Which  orders  derive  their  names  from  anatomic  features? 

16.  Which  orders  are  aquatic? 


1 8  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

17.  What  is  the  ultimate  syllable  of  all  family  names? 

18.  Explain  what  is  meant  by  binomial  nomenclature. 

19.  Name  three  families  of  Carnivora. 

20.  Examine  specimens  and  determine  wherein  the  teeth  of  Canidse 
differ  from  those  of  Felidae. 

21.  What  two  rank  names  constitute  the  scientific  name  of  an  animal? 

22.  Give  the  scientific  name  of  five  Carnivora,  two  Ungulata,  and 
two  Primates. 

23.  Define  organ,  system,  tissue,  and  cell. 

24.  Name  two  organs  belonging  to  each  system. 

25.  How  do  the  elements  of  the  four  kinds  of  tissue  differ? 

EXTERNAL    FEATURES. 

The  cat,  like  all  other  mammals,  possesses  two  well- 
defined  skeletons,  the  endoskeleton,  consisting  of  the  true 
bones,  and  the  exoskeleton,  composed  of  the  skin  and  its 
appendages.  The  skin  invests  the  body  completely  and  is 
continuous  with  the  lining  of  the  digestive  and  urogenital 
canals.  It  varies  in  thickness  in  different  regions,  being 
very  thin  on  the  lips,  ears,  and  eyelids,  and  exceedingly 
thick  on  the  pads  of  the  feet  and  on  the  ventral  neck  region, 
where,  in  contest  with  an  enemy,  it  is  most  likely  to  be 
seized.  A  fibrous  connective  tissue  binds  the  skin  to  the 
subjacent  structures.  In  some  places  the  union  is  very 
firm,  as  on  the  distal  parts  of  the  limbs  and  the  head,  while 
in  other  regions  it  is  loose,  as  on  the  lateral  aspect  of  the 
trunk. 

The  skin  consists  of  an  external  layer,  the  epidermis,  and 
beneath  this,  the  dermis  or  true  skin,  designated  the  corium. 
The  epidermis  is  composed  of  numerous  strata  of  epithelial 
cells.  Those  on  or  near  the  surface  are  much  flattened 
while  the  deeper  ones  are  more  or  less  cubical.  As  the 
superficial  layer  desquamates  in  minute  fragments,  forming 
what  is  commonly  called  dandruff,  it  is  replaced  by  cells 
developed  from  the  deeper  layers. 

At  the  orifices  of  the  internal  passages,  such  as  the  diges- 


GENERAL  STRUCTURE.  19 

tive  and  genital  tracts,  the  epithelium  changes  to  a  soft 
delicate  nature,  and  is  then  known  throughout  these  pas- 
sages as  mucous  membrane. 

The  corium  or  dermis  is  a  form  of  fibrous  connective 
tissue  whose  deepest  portion  forms  the  white  fluffy  areolar 
substance  cut  in  removing  the  skin.  In  many  regions  just 
below  the  true  skin  is  a  layer  of  adipose  tissue,  which  when 
examined  under  the  microscope  is  seen  to  be  composed  of 
numerous  globular  fat-cells  supported  by  fibrous  areolar 
tissue.  The  seven  pads  on  the  forepaw  and  the  five  on  the 
hind  one  consist  of  greatly  thickened  epidermis,  the  corium, 
and  masses  of  fibrous  connective  tissue  enveloping  many 
fat-cells. 

The  sebaceous  or  oil  glands  lie  in  the  corium,  and  by 
means  of  a  duct  open  into  the  hair  follicle  near  the  sur- 
face. The  sudoriparous  or  sweat  glands,  composed  of 
coiled  tubes,  are  present  in  the  subcutaneous  tissue,  from 
whence  a  duct  extends  to  the  surface.  Although  there  are 
no  blood-vessels  in  the  epidermis,  numerous  nerve  termina- 
tions are  present  in  the  deeper  portions.  The  true  skin  is 
richly  supplied  with  both  nerves  and  blood-vessels. 

The  claws  produced  by  a  special  modification  of  the 
epidermis  are  among  the  most  important  appendages  of  the 
skin.  Five  of  these  are  present  on  each  forefoot,  while  only 
four  occur  on  the  hind  one.  At  the  root  of  each  claw, 
the  dermis  forms  a  crescentic  fold  over  it,  and  beneath  is  a 
number  of  papillae  richly  supplied  with  blood-vessels.  This 
entire  structure  forms  the  matrix  of  the  claw,  which  is  set 
around  the  terminal  part  of  the  distal  phalanx  of  each  digit. 
Claws,  or  some  similar  structures,  such  as  nails  or  hoofs, 
are  present  in  all  mammals  except  the  Cetacea. 

Another  important  appendage  of  the  skin  is  the  hair, 
which  covers  the  entire  body  except  the  tip  of  the  nose  and 
the  pads  of  the  feet.  Its  length  and  color  vary  with  the 


20  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

variety  of  the  cat.  The  Mombus  cat  of  Africa  has  short 
stiff  hair,  while  the  Angora  or  Persian  cat  is  remarkable  for 
the  length  and  delicacy  of  its  soft  fur.  The  hair,  like  the 
nails,  is  an  extreme  modification  of  the  epidermis.  Each 
hair  grows  from  a  .papilla  at  the  bottom  of  a  small  sac,  the 
follicle,  which  is  a  depression  in  the  corium.  The  central 
part  of  the  hair  is  the  pith,  and  the  external  portion,  formed 
of  thin  overlapping  scales,  the  cuticle.  The  coloring-matter 
lies  in  the  superficial  scales,  and  may  be  disposed  in  such  an 
irregular  manner  that  one-half  of  a  hair  is  white,  and  the 
other  half  yellow. 

The  large  hairs  on  either  side  of  the  nose  are  known 
as  vibrissce.  Their  roots  are  provided  with  delicate  nerve- 
endings  of  touch,  so  that  the  animal  may  find  its  way  with 
ease  through  dark  narrow  passages.  There  are  a  few  long 
hairs  above  the  eyes,  forming  the  eyebrows,  but  no  eye- 
lashes are  present. 

Most  of  the  hairs  are  inserted  obliquely  into  the  skin, 
but  when  angered  the  cat  can  erect  them  by  the  contraction 
of  a  small  muscle  passing  from  the  skin  to  the  hair-bulb. 

On  some  mammals  the  hairy  covering  is  partial  and 
limited  to  particular  regions ;  in  others,  as  the  hippopotamus 
and  the  Sirenia,  it  is  very  scanty,  but  scattered  over  the 
whole  surface;  while  in  the  Cetacea  it  is  reduced  to  a  few 
small  bristles  about  the  mouth. 

Some  kinds  of  hair,  as  those  of  the  mane  and  tail  of  the 
horse,  are  shed  and  renewed  annually.  Most  mammals 
have  a  long  hairy  coat  in  winter  which  gives  place  in  spring 
to  a  short  coat.  The  Arctic  fox,  hare,  ermine,  and  numer- 
ous other  animals  of  the  colder  regions  undergo  a  complete 
change  of  color  in  the  two  seasons,  being  white  in  winter 
and  brown  or  gray  in  summer.  By  this  protective  colora- 
tion they  escape  many  of  their  enemies. 


THE  SKELETON. 

The  number  of  bones  in  the  skeleton  of  the  cat  varies 
with  its  age,  since  two  or  more  bones  separate  in  the  young 
may  form  one  mass  in  the  old  animal.  The  three  portions 
of  the  innominate  bone  which  are  distinct  (Fig.  38)  in  the 
young,  become  fused  in  the  adult.  In  very  old  age  many 
sutures  of  the  skull  become  partially  or  wholly  obliterated. 
In  the  young  adult  cat  the  number  of  bones,  exclusive  of  the 
teeth,  ear  bones,  chevron  bones,  and  sesamoid  bones,  is 
about  233.  The  sacrum  is  reckoned  as  one  bone,  though 
composed  of  three  coalesced  vertebrae.  The  structure  and 
embryology  of  the  teeth  show  that  they  belong  to  a  different 
category  from  the  bones.  The  ossicula  auditus,  or  ear 
bones,  are  the  malleus,  incus,  and  stapes  of  the  middle  ear. 
The  chevron  bones  are  eight  in  number,  attached  to  the 
ventral  side  of  the  vertebrae  of  the  tail.  The  sesamoid  bones 
number  about  forty,  of  which  the  patella,  or  knee-cap,  is  the 
largest.  They  are  formed  in  the  tendons  where  there  is 
much  pressure  or  friction,  as  upon  the  volar  surface  of  the 
metacarpus.  The  outline  on  page  22  gives  the  classifica- 
tion, names,  and  number  of  the  different  bones  of  the 
skeleton. 

GENERAL  TERMS  USED  IN  DESCRIPTION  OF 

BONES. 

In  reference  to  shape  the  bones  are  spoken  of  as  long, 
short,  flat,  and  irregular.  Long  bones  are  those  having  a 
shaft  or  diaphysis  in  which  is  a  cavity  filled  with  marrow, 
and  two  enlarged  extremities  or  epiphyses  (Fig.  13)  : 
femur,  fibula,  metacarpals,  and  phalanges.  Short  bones 

21 


22 


ELEMENTS    OF   MAMMALIAN    ANATOMY. 


r  Skull 


Head 


AXIAL  SKELE- 


r  Cranium 

« 


Face 


Frontal 2 

Ethmoid, 1 

Temporal 2 

Parietal,    ...  2 

Interparietal,  ....  1 

Occipital 1 

Sphenoid, 1 


Premaxillary, .  . 
Maxillary,    .   .   . 

Palatine 

Vomer,  .... 
Maxilloturbinal . 

Nasal 

L,achrymal  •    •   • 
Malar  or  Jugal, 
Mandible 


APPENDICU- 
LAR  SKELE- 
TON 


Tympanohyal,  ...  2 
Stylohyal 2 

Hyrfd  bones  ^    SSSfti'.  I  I  T  I   I 

Basihyal, 1 

Thyrohyal 2 

{Cervical  vertebrae,  .  7 
Thoracic  vertebrae,  .  13 
lumbar  vertebrae,  .  7 
Sacral  vertebrae,  .  .  1 
Caudal, 21 

/  Ribs,  .........  26 

Thorax  ,  (  sternum,  ......    1 

shoulder  girdle  f§ggg|;  ;  ;  ;  ;  ;  ;  2 

Arm  Humerus,  , 2 

/  Ulna 2 

Forearm  (  Radius, 2 

-  Thoracic  limb    <|                                                   Scapholunar, 2 

Cuneiform, 2 

Pisiform 2 

Carpus           •<    Trapezium 2 

Trapezoid 2 

Magnum 2 

Unciform, 2 

Hand 

Metacarpus  10 

(  Proximal, 10 

Phalanges       -I  Middle, 10 

(  Distal, 8 

,.   Pelvic  girdle  Innominate,    ....   2 

f  Femur, 2 

I,eg  J    Patella 2 

1    Tibia 2 

^  Fibula 2 

Pelvic  limb        J  Astragalus 2 

Calcaneum 2 

Scaphoid 2 

Tarsus  •<    Internal  cuneiform..  2 

Middle  cuneiform,  .  2 
External  cuneiform,  2 

Cuboid, 2 

Foot 

Metatarsus  10 


^  Phalanges 


Proximal 8 

Middle 8 

Distal 8 


THE   SKELETON. 


23 


are  those  not  elongated  and  with  no  medullary  cavity: 
tarsus  and  carpus.  Flat  bones  are  plate-like,  with  a  layer- 
of  cancellous  tissue  between  two  layers 
of  compact  tissue :  parietal,  scapula, 
and  innominate.  Irregular  bones  are 
those  which  have  an  exceedingly  ir- 
regular shape :  ethmoid  and  vertebrae. 
The  aspect  of  a  bone  is  the  portion 
seen  when  viewed  from  a  given  direc- 
tion. The  bQrder  of  a  bone  is  the 
margin,  edge,  or  ridge  at  the  juncture 
of  two  surfaces.  Proximal  is  used  to 
designate  the  portion  of  a  structure 
nearer  the  axis  or  spinal  column,  in 
distinction  to  distal,  which  signifies  the 
part  farther  removed  from  the  axis. 
Cranial  indicates  the  part  of  an  organ 
nearer  to  the  plane  passing  just  beyond 
the  head  and  perpendicular  to  the  spinal 
axis,  while  caudal  is  applied  to  the 
other  part  of  the  organ  nearer  to  the 
perpendicular  plane  at  the  end  of  the 
extended  tail. 

Sagittal  refers  to  the  plane  bisecting 
the  animal  in  a  vertical  and  longitudi- 
nal direction.  Medial  and  lateral  are 
adjectives,  the  former  meaning  nearer 
to  the  sagittal  plane  and  the  latter  more 
remote  on  either  side  of  that  plane. 
Proximad,  distad,  craniad,  caudad, 
mediad  and  laterad  are  adverbs  indicating  direction  in  ac- 
cordance with  the  adjectives  to  which  they  are  related. 

A  process  is  projection  or  elevation. 

A  tuberosity  is  a  rough  obtuse  process. 


FIG.     12.       LONGITU- 
'  DINAL    SECTION    OF 
THE  HUMERUS  OF  A 
KITTEN. 

h,  Epiphysis  for  head ; 
c,  cartilage ;  b,  bone ; 
m,  medullary  sub- 
stance; o,  epiphysis 
for  olecranon  proc- 
ess. 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


A  tubercle  is  a  small  and  usually  more 
or  less  pointed  process. 

A  condyle  is  a  rounded  and  somewhat 
elongated  smooth  articular  process.  The 
distal  end  of  the  femur  presents  a  pair 
of  condyles  (Fig.  40). 

A  fossa  is  an  irregular  depressed  area 
(Fig.  30). 

A  foramen  is  an  aperture  for  the  pas- 
sage of  vessels  or  nerves. 

The  shaft  is  the  body  or  middle  por- 
tion of  an  elongated  bone. 

The  head  is  a  spheroidal  prominence 
at  one  end  of  an  elongated  bone  (Fig. 
40). 

The  epiphysis  is  a  small  process  of 
bone  ossified  from  a  separate  center.  In 
the  young  animal  it  is  attached  to  the 
main  bone  by  cartilage,  but  in  the  adult 
becomes  a  part  of  the  main  bone  (Fig. 
12).  The  femur  has  four  epiphyses, 
one  for  the  head,  one  for  the  distal  ex- 
tremity, and  one  for  each  trochanter  proc- 
ess (Fig.  40).  With  the  exception  of 
the  phalanges,  metacarpals,  and  metatar- 
sals,  all  of  the  long  bones  have  an  epi- 
physis at  each  extremity.  In  the  human, 
these  epiphyses  do  not  unite  with  the 
shaft  before  the  sixteenth  year.  Diploe 
is  the  spongy  layer  of  bone  between  the 
compact  surface  layers  of  the  flat  bones 
(Fig.  18). 

The  articulation  of  a  bone  has  reference  to  its  contact 
with  other  bones  by  means  of  joints. 


FIG.  13.  LONGI- 
TUDINAL SECTION 
OF  THE  FEMUR. 

md,  Medullary  cav- 
ity; d  and  h, 
cancellous  t  i  s  - 
sue;  tr,  cancel- 
lous tissue  of 
trochanter  proc- 
ess ;  b,  compact 
bony  tissue. 


THE   SKELETON.  25 

STRUCTURE  OF  BONE. 

Every  bone  is  completely  covered  except  on  its  articu- 
lating surfaces  with  a  tough  membrane,  the  periosteum, 
which  serves  for  the  attachment  of  muscles,  and  the  renewal 
of  bony  tissue  in  case  of  injury.  The  long  bones  contain  a 
cavity,  the  medullary  cavity,  filled  with  marrow  (Fig.  12). 


FIG.  14.     CROSS-SECTION  OF  CAT'S  FEMUR.     X  5. 

cp,  Compact  tissue ;  en,  cancellous  tissue ;  en,  endosteum ;  me,  medullary 
canal ;  pe,  periosteum. 

This  cavity  is  lined  with  endosteum,  a  membrane  similar  to 
the  periosteum. 

The  shaft  of  the  long  bone  is  composed  mainly  of  com- 
pact bony  tissue  through  which  extend  longitudinally  inter- 
communicating microscopic  channels,  Haversian  canals,  for 
the  conveyance  of  blood-vessels,  nerves,  and  lymphatics. 

The  lacunce,  or  spaces  for  the  bone  cells  during  life,  are 
arranged  concentrically  about  the  Haversian  canals.  The 
canaliculi,  or  processes  of  the  lacunae,  communicate  with  one 
another.  At  the  extremities  of  the  bones  the  place  of  the 
medullary  canal  is  taken  up  by  cancellous  tissue  (Fig.  13, 
d),  the  compact  tissue  being  very  thin.  The  flat  bones  have 
no  medullary  canal,  but  the  diploe  or  cancellous  tissue  lying 
between  the  outer  compact  tissue  has  its  spaces  filled  with  a 

4 


26  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

red  marrow  of  the  same  nature  as  that  in  the  cancellous 
tissue  of  the  long  bones,  wherein  the  red  blood-corpuscles 
are  formed.  The  large  medullary  cavity  or  canal  is  filled 
with  yellow  or  fatty  marrow. 

BONES  OF  THE  SKULL. 

The  skull  is  usually  considered  in  two  parts,  the  cranium 
and  face.  The  former  is  composed  of  nine  bones,  which 
will  be  described  in  order. 

The  frontal  bones  (Figs.  15  and  16)  are  two  in  number, 
lying  between  the  orbits,  and  articulating  with  one  another 
in  the  median  line.  They  form  the  roof  of  the  cranial  part 
of  the  brain  cavity  and  the  caudal  portion  of  the  roof  of 
the  nasal  chamber.  A  lateral  projection  (po,  Fig.  16)  is 
known  as  the  postorbital  process.  Within  the  frontal  bone 
is  a  cavity,  the  frontal  sinus  (Fig.  18),  which  contains  air 
and  is  lined  with  mucous  membrane.  It  communicates  with 
the  nasal  cavity.  The  lateral  descending  portion  of  the 
bone,  articulating  with  the  palatine  and  orbitosphenoid,  is 
the  orbital  plate  of  the  frontal. 

In  the  majority  of  the  Mammalia  the  frontal  is  a  paired 
bone,  but  in  man  the  two  portions  become  anchylosed  dur- 
ing the  fifth  or  sixth  year.  The  horns  of  ruminants  are 
outgrowths  of  these  bones.  Among  the  Cervidse  (deer) 
horns  are  usually  developed  only  on  the  male,  and  are  shed 
every  year.  In  the  Bovidse  (cattle)  the  horns  are  perma- 
nent when  present. 

The  ethmoid  (Fig.  18)  is  a  single  bone  lying  ventral  to 
the  frontals  and  nasals.  It  separates  the  cranial  cavity 
from  the  nasal  cavity  and  projects  into  the  latter  in  the 
form  of  two  thin  scroll-like  plates  of  bone  and  a  median 
vertical  plate.  In  order  to  see  the  relations  of  this  bone, 
three  skulls  must  be  used,  one  of  which  should  be  bisected 
sagittally,  a  second  should  have  the  roof  of  the  cranial  and 


THE   SKELETON. 


nasal  cavities  removed,  and  the  third  should  be  cut  trans- 
versely on  a  line  joining  the  middle  of  the  orbits.  The_ 
ethmoid  is  usually  visible  externally  as  a  small  rhomboid 
plate  on  the  medial  wall  of  the  orbit  between  the  frontal, 


barichd          [w*^ 
A  I  MES 


f-m^    *upft?/4«*     7}a2a.2itte 


FIG.  15.     DIAGRAM  OF  THE  BONES  OF  THE  MAMMALIAN  SKULL  VIEWED 

LATERALLY. 
i,  2,  3,  etc.,  indicate  the  places  of  exit  of  the  twelve  cranial  nerves,    pmx, 

Premaxillary ;  ty,  tympanic,  7  and  8  are  on  periotic;  thy,  tympano- 

hyal;  shy,  stylohyal ;  ehy,  epihyal;  chy,  ceratohyal ;  bhy,  basihyal ; 

thhy,  thyrohyal.     The  cartilage  bones  are  shaded. —  {From  Flower, 

after  Huxley.) 

lachrymal,  and  palatine  bones.  It  consists  of  four  parts: 
the  paired  ethmoturbinals  or  lateral  ethmoids  (Fig.  18), 
the.  mesethmoid,  and  the  cribriform  plate.  The  ethmotur- 
binals are  in  the  form  of  scroll-like  laminae  which  project 
forward  from  the  transverse  cribriform  plate  into  the  nasal 
cavities.  The  portion  which  appears  externally  in  the 
medial  wall  of  the  orbit  is  the  os  planum.  In  the  recent 
state,  the  surfaces  of  these  bones  within  the  nasal  cavity  are 
covered  with  a  mucous  membrane  over  which  the  first  pair 
of  cranial  nerves  (olfactory)  are  distributed.  The  delicacy 


28  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

of  tlie  sense  of  smell  is  proportional  to  the  development  of 
the  ethmoturbinals.  In  most  orders  of  animals  five  scrolls 
are  present,  but  in  Echidna  there  are  six  and  in  some  Ungu- 
lates there  are  eight,  while  in  adult  Primates  there  are  only 
from  one  to  three,  more,  however,  being  present  in  the 
embryo. 

The  mesethmoid  is  the  perpendicular  plate  of  bone  which, 
prolonged  craniad  by  cartilage,  separates  the  nasal  cavity 
into  two  portions.  Caudad  it  is  united  to  the  cribriform 


FIG.  16.    DORSAL  ASPECT  OF  THE  CAT'S  SKULL. 

ap,  Anterior  palatine  foramen;  c,  canine  tooth;  co,  coronal  suture;  /, 
foramina  in  palatine  bone,  the  lateral  one  is  the  posterior  palatine 
and  the  medial  one  is  the  sphenopalatine ;  fr,.  frontal ;  if,  inf raorbital 
foramen ;  in,  interparietal ;  Ic,  lachrymal  canal  at  the  medial  border 
of  the  lachrymal  bone ;  Id,  lambdoidal  crest ;  ml,  malar ;  mx,  maxil- 
lary; na,  nasal;  oc,  occipital;  p,  vertical  plate  of  the  palatine;  po, 
postorbital  process  of  the  frontal;  pm,  postorbital  process  of  the 
malar;  par,  parietal;  px,  premaxillary;  sq,  squamosal  part  of  the 
temporal;  sg,  sagittal  suture;  j/>,  alisphenoid  part  of  the  sphenoid; 
tp,  temporal  fossa ;  sg,  zygomatic  process  of  the  squamosal. 

plate,   dorsally   it  articulates   with   the   median   descending 
plates  of  the  frontals  and  the  nasals,  and  ventrally  it  articu- 


THE   SKELETON.  29 

lates  with  the  vomer  and  presphenoid.  The  cribriform 
plate  is  the  caudal  portion  of  the  ethmoid  (Fig.  18),  which,, 
extending  transversely  between  the  frontals,  separates  the 
cranial  cavity  from  the  nasal  cavity.  It  is  pierced  by  many 
pinhole  foramina  for  the  exit  of  the  olfactory  nerve.  In 
Ornithorhynchus  (duck-bill  of  Australia)  there  is  a  single 
large  foramen  in  the  cribriform  plate,  as  is  also  the  case  in 
birds. 

The  temporal  is  a  paired  bone  lying  at  the  base  and  side 
of  the  skull.  It  contains  the  organs  of  hearing.  It  con- 
sists of  four  parts :  the  squamous  or  expanded  portion  (Fig. 
16),  to  which  .the  sygomatic  process  is  attached;  the  mastoid 
(Fig.  17),  which  is  the  part  caudad  of  the  squamosal  and 
dorsal  to  the  bulla;  the  tympanic,  which  forms  the  auditory 
bulla;  and  the  petrous  (Figs.  17  and  18),  which  contains  the 
internal  ear.  The  squamous  portion  overlaps  the  parietal 
dorsally  in  a  scale-like  manner  and  is  limited  ventrally  by 
a  clearly  defined  projecting  ridge  extending  above  the 
external  auditory  meatus  as  the  dorsal  border  of  the 
zygoma. 

The  sygomatic  process  extends  craniad  to  join  the  zygo- 
matic  process  of  the  malar,  the  two  together  forming  the 
sygomatic  arch,  or  zygoma,  to  which  the  masseter  muscle  is 
attached.  Ventral  of  the  root  of  the  zygomatic  process  is 
the  glenoid  cavity  for  the  articulation  of  the  condyle  of 
the  mandible.  Immediately  caudad  of  this  cavity  is  the 
postglenoid  process.  The  mastoid  portion  of  the  bone  is 
somewhat  triangular  in  shape,  about  two  centimeters  long, 
and  lies  caudad  of  the  external  meatus. 

The  tympanic  portion  appears  on  the  base  of  the  skull 
as  the  auditory  bulla.  Its  cavity  is  divided  into  two  unequal 
chambers  by  a  bony  septum  rising  from  the  floor  and  reach: 
ing  almost  to  the  roof.  The  cranial  or  true  tympanic 
chamber,  sometimes  called  the  middle  ear,  is  the  smaller, 


3°  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

and  has  on  its  lateral  wall  a  horseshoe-shaped  prominence 
known  as  the  tympanic  ring,  to  which  the  tympanic  mem- 
brane of  the  drum  of  the  ear  is  attached.  There  are  four 
apertures  in  the  walls  of  the  cranial  tympanic  chamber :  The 
meatus  auditorius  externus,  or  the  external  auditory  canal ; 
the  Eustachian  tube,  leading  from  the  cranial  dorsal  angle 
of  the  chamber  to  the  pharynx;  the  fenestra  ovalis  and  the 
fenestra  rotundum,  opening  into  the  internal  ear.  The 
caudal  or  medial  chamber  of  the  bulla  is  larger  than  the 
cranial,  but  has  no  special  features  worthy  of  consideration. 

The  petrous  portion  of  the  temporal  bones  is  not  visible 
on  the  external  surface  of  the  skull,  but  may  be  seen  by 
looking  into  the  external  auditory  meatus.  It  forms  the 
medial  wall  of  the  tympanic  cavity.  The  foramen  seen  in 
its  dorsal  part  is  the  fenestra  ovalis.  In  a  sagittally  bi- 
sected skull  the  petrous  (Fig.  17)  may  be  recognized  by  the 
internal  auditory  meatus  entering  it.  By  removing  the 
bulla,  a  large  portion  of  the  petrous  bone  may  be  seen  from 
its  ventral  aspect.  A  central  prominence,  the  promontory, 
contains  the  fenestra  rotundum  opening  into  the  base  of  the 
cochlea.  The  apex  of  the  promontory,  mediad  of  the 
fenestra  rotundum,  forms  the  wall  of  the  first  whorl  of  the 
cochlea.  Dorsal  to  the  fenestra  rotundum  is  the  fenestra 
ovalis,  opening  into  the  vestibule  of  the  internal  ear.  In 
the  recent  state  this  opening  is  closed  by  a  membrane  in 
which  is  imbedded  the  foot  of  the  stapes.  The  cochlea  in 
the  interior  of  the  bone  may  be  displayed  by  cutting  away 
the  bony  rim  of  the  fenestra  rotundum  and  then  chipping 
off  a  crust  of  bone  in  a  line  from  this  foramen  to  the  junc- 
ture of  the  basioccipital  and  basisphenoid  bones. 

The  petrous  bone,  viewed  dorsally  in  a  bisected  skull, 
appears  in  the  floor  of  the  brain  cavity  ventrad  of  the  ten- 
torium,  the  plate  of  bone  partly  separating  the  cerebrum 
from  the  cerebellum.  Its  surface  is  pierced  by  the  internal 


THE   SKELETON.  31 

auditory  meatus,  which  gives  passage  to  the  auditory  nerve. 
Close  examination  reveals  a  division  of  the  canal  into  two 
parts,  a  ventral  for  the  eighth  nerve  and  a  dorsal,  the  aque- 
ductus  Fallopii,  for  the  facial  nerve.  This  aqueduct  twists 
through  the  petrous  laterad,  and  thence  between  the  petrous, 
squamosal,  and  mastoid  to  the  stylomastoid  foramen  (Fig. 

17)- 

The  parietal  bone  is  paired  and  joins  its  fellow  in  the 
median  line,  forming  the  caudal  half  of  the  sagittal  suture. 
Its  point  of  greatest  convexity  is  the  parietal  eminence.  Its 
cerebral  or  internal  surface  presents  slight  arborescent 
grooves  which  in  the  recent  state  sheltered  the  meningeal 
artery  of  the  brain.  The  plate  of  bone  projecting  obliquely 
craniad  from  the  caudal  border  of  the  parietal  is  the  tento- 
riuni,  an  ossification  of  the  dura  mater  separating  the  cere- 
brum from  the  cerebellum. 

The  interparietal  is  a  triangular  bone  situated  at  the 
junction  of  the  two  parietals  and  occipital  bones.  Its 
sutures  are  usually  obliterated  quite  early. 

The  occipital  (Figs.  16,  17,  and  18)  is  a  single  bone 
surrounding  the  foramen  magnum  and  articulating  with 
the  interparietal,  parietals,  temporals,  and  sphenoid.  In  the 
young  kitten  it  is  composed  of  four  parts :  the  supraocci- 
pital,  lying  dorsal  to  the  foramen  magnum,  the  two  exocci- 
pitals,  lying  laterad  of  it,  and  a  basioccipital,  bounding  it 
ventrally.  The  crescentic  elevation  on  the  supraoccipital 
near  its  parietal  margin  is  the  lanibdoidal  ridge,  to  which 
several  muscles  are  attached. 

The  exoccipitals  bound  the  cerebellum  laterally  and  sup- 
port the  occipital  condyles,  which  articulate  with  the  atlas 
or  first  vertebra.  Immediately  caudad  of  the  bulla  is  the 
par  occipital  process.  There  are  two  foramina,  one  of 
which,  the  anterior  condyloid,  opens  ventrally  with  the  jug- 
ular foramen  adjacent  to  the  bulla,  while  the  other,  the 


ELEMENTS   OF   MAMMALIAN   ANATOMY. 
1C 


prn 


•19 


FIG.   17.    VENTRAL  ASPECT  OF  THE  SKULL  WITH  THE  LEFT  AUDITORY 
BULLA  REMOVED. 

asp,  Alisphenoid ;  ap,  anterior  palatine  foramina ;  bs,  basisphenoid ;  bl, 
auditory  bulla;  bo,  basioccipital ;  c,  canine  tooth;  ^petrous  portion 
of  the  temporal;  en,  occipital  condyle;  ea,  external  auditory  meatus; 
eh,  opening  of  the  Eustachian  tube ;  fr,  frontal ;  fm,  foramen  mag- 
num; gc,  glenoid  cavity;  gn,  postglenoid  process;  hm,  hamular  proc- 
ess of  the  pterygoid;  ic,  incisor  tooth;  if,  infraorbital  foramen;  in, 
incus;  jg,  jugular  foramen;  Id,  lambdoidal  ridge;  mx,  maxilla;  ml, 
molar  tooth ;  mp,  mastoid  process ;  ms,  mastoid  portion  of  the  tem- 
poral ;  ma,  malar ;  m,  malleus ;  osp,  orbitosphenoid ;  ov.  foramen 


THE   SKELETON.  33 

posterior  condyloid,  opens  more  dorsally  at  the  side  of  the 
condyle.  The  former  transmits  the  twelfth  (hypoglossal)^ 
cranial  nerve,  supplying  the  larynx,  hyoid  bone,  and  tongue. 
The  jugular  foramen,  or  foramen  lacerum  posterius,  is  at 
the  juncture  of  the  bulla,  exoccipital,  and  basioccipital. 
The  internal  jugular  vein  and  the  ninth,  tenth,  and  eleventh 
nerves  pass  through  it.  The  basioccipital  portion  of  this 
bone  lies  entirely  on  the  ventral  aspect  of  the  skull.  It 
articulates  craniad  with  the  basisphenoid  by  a  suture  which 
is  generally  obliterated  in  cats  three  or  four  years  old. 

The  sphenoid  bone  lies  in  the  center  of  the  base  of  the 
skull.  It  is  composed  of  eight  parts,  corresponding  to  eight 
distinct  bones  in  the  lower  vertebrates:  the  basisphenoid, 
articulating  caudad  with  the  basioccipital ;  two  alisphenoids, 
extending  dorsad  from  the  basisphenoid  and  articulating 
caudad  with  the  temporals  (Figs.  17  and  18)  two  ptery- 
goids,  projecting  ventrally  from  the  basisphenoid  and 
terminating  in  sharp  processes;  a  presphenoid  in  the  mid- 
ventral  line  craniad  of  the  basisphenoid;  two  orbitosphen- 
oids,  extending  dorso-laterally  from  the  presphenoid  and 
articulating  craniad  with  the  frontals.  In  an  old  cat,  the 
sutures  between  these  eight  parts  become  more  or  less  oblit- 
erated. The  basisphenoid  together  with  the  alisphenoids 
is  sometimes  called  the  posterior  sphenoid  in  distinction  to 
the  anterior  sphenoid,  composed  of  the  presphenoid  and 
orbitosphenoids. 

The  basisphenoid  presents  on  its  dorsal  or  cerebral  sur- 
face the  sella  turcica,  or  pituitary  fossa,  which  lodges  the 
pituitary  body  of  the  brain  (Fig.  9$).  The  posterior 
boundary  of  this  fossa  is  the  clinoid  plate,  and  its  lateral 

ovale;  p,  presphenoid;  pi,  palatine;  pi,  pterygoid;  pn,  promontory 
of  the  petrous ;  po,  postorbital  process ;  pr,  premolar  teeth ;  pm, 
premaxillary ;  rd,  fenestra  rotundum;  rt,  foramen  rotundum;  st, 
stapes ;  sg,  squamosal ;  sf,  stylomastoid  foramen ;  if,  carotid 
foramen,  or  foramen  lacerum  medius ;  vm,  vomer,  forming  the 
septum  between  the  posterior  nares ;  sg,  zygornatic  process  of 
squamosal. 


34 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


projections  are  the  posterior  clinoid  processes.  On  each 
side  of  the  basisphenoid  there  extends  dorsally  in  a  narrow 
strip  to  the  parietal  the  alisphenoid,  at  the  base  of  which, 
craniad  of  the  auditory  bulla,  are  three  foramina  in  a  line. 
The  most  cranial  and  largest  one  is  the  sphenoidal  fissure, 
or  anterior  lacerated  foramen,  which  transmits  the  third, 
fourth,  and  sixth  cranial  nerves  supplying  the  eyeball 
muscles,  and  the  first  branch  of  the  fifth  nerve.  This 
foramen  is  between  the  alisphenoid  and  the  orbitosphenoid. 
The  other  two  foramina,  rotundum  and  ovale,  transmit  the 
second  and  third  divisions  of  the  fifth  nerve. 

TABLE  OF  THE  FORAMINA  OF  THE  SKULL. 


FORAMINA. 

BONES  SURROUNDING 
THE  FOKAMINA. 

STRUCTURES  TRAVERSING  THE 

FORAMINA. 

Infraorbital. 

Superior  maxillary 

Infraorbital   nerve   of   the   su- 

perior maxillary  division  of 

the  fifth. 

Anterior  palatine. 

Maxillary  and  pre- 

Nasopalatine     branch     of     the 

maxillary. 

fifth  cranial  nerve  and  nasal 

artery. 

Sphenopalatine. 

Palatine. 

Sphenopalatine       nerve       and 

sphenopalatine  artery. 

Posterior  palatine. 

Palatine. 

Palatine  nerve  and  artery. 

Olfactory  fora- 

Ethmoid. 

Olfactory  nerve. 

mina. 

Optic. 

Orbitosphenoid. 

Optic     nerve     and     meningeal 

artery. 

Lacerum   anterius, 

Alisphenoid  and 

Third,  fourth,  and  sixth  cranial 

or  sphenoidal  fis- 

orbitosphenoid. 

nerves   and   first  division  of 

sure. 

fifth   cranial    nerve. 

Rotundum. 

Alisphenoid. 

Second  division  of  fifth  cranial 

nerve, 

Ovale. 

Alisphenoid. 

Third  division  of  fifth  cranial 

nerve. 

Lacerum  medium. 

Petrous   and  basi- 

Internal  carotid   artery. 

sphenoid. 

Internal     auditory 

Petrous. 

Eighth  cranial  nerve. 

meatus. 

Aqueduct  of  Fallo- 

Petrous,    mastoid, 

Seventh  cranial  nerve. 

pius. 

and  tympanic. 

Stylomastoid. 

Tympanic  and 

Seventh  cranial  nerve. 

mastoid. 

Jugular  or  poster- 

Occipital and  tem- 

Ninth,    tenth,     and     eleventh 

ior  lacerated. 

poral. 

cranial    nerves    and    jugular 

vein. 

Anterior  condyloid 

Exoccipital. 

Twelfth  cranial  nerve. 

THE   SKELETON. 


35 


The  pterygoid  portion  of  the  sphenoid  is  a  paired  bone 
(Figs.  17  and  18)  lying  on  either  side  of  the  cranial  half 
of  the  basisphenoid  and  the  caudal  half  of  the  presphenoid. 


In  the  adult  cat  the  sutures  are  sometimes  obliterated  so 
that  this  bone  appears  as  a  caudal  continuation  of  the  pala- 
tine. The  two  pterygoid  bones  or  plates  form  the  descend- 
ing walls,  and,  together  with  the  median  portion  of  the 


36  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

sphenoid,  the  roof  of  the  median  pterygoid  fossa,  whose 
cranial  continuation  is  the  posterior  nares.  From  the  ven- 
tral posterior  angle  of  each  projects  the  hamular  process, 
dorsal  of  which  is  seen  the  small  external  pterygoid  process. 
Between  the  bases  of  the  hamular  and  the  external  ptery- 
goid processes  is  the  small  external  pterygoid  fossa. 

The  presphenoid  bone  is  the  narrow  median  bone  extend- 
ing from  the  basisphenoid  to  the  vomer.  It  contains  within 
it  two  large  sinuses  into  which  project  the  ventral  scrolls 
of  the  ethmoturbinal  bones.  The  orbitosphenoids  enter 
into  the  formation  of  the  medial  walls  of  the  orbits  and  are 
perforated  at  their  bases  by  the  optic  foramina,  through 
which  pass  the  optic  nerves. 

BONES  OF  THE  FACE. 

There  are  seven  paired  bones  in  the  face  and  two  single 
ones,  making  in  all  sixteen  (Figs.  16  and  17). 

The  premaxillary,  with  its  fellow,  extends  ventrad  and 
laterad  of  the  anterior  nares.  These  bones  bear  the  six 
incisor  teeth.  The  anterior  palatine  or  incisor  foramina 
connect  the  oral  cavity  with  that  of  the  anterior  nares.  In 
life,  these  foramina  transmit  the  naso-palatine  nerves.  In 
the  Primates,  the  premaxillary  is  anchylosed  to  the  maxil- 
lary although  it  arises  from  a  separate  center  of  ossification. 

The  maxillary  is  a  paired  bone  which  meets  its  fellow 
in  the  median  line  in  the  roof  of  the  mouth.  All  its  articu- 
lations are  visible  externally  except  those  with  the  maxillo- 
turbinal,  ethmoid,  and  vomer.  Five  teeth,  a  canine,  three 
premolars,  and  a  molar,  are  present  in  this  bone  of  the 
adult  cat.  The  molar  is  wanting  to  the  young.  The  several 
portions  of  the  bone  are  as  follows:  the  palatine  plate, 
appearing  in  the  roof  of  the  mouth;  the  nasal  process,  ex- 
tending dorso-caudad  to  the  frontal ;  the  malar  process,  ex- 
tending ventrad  to  the  orbit  to  articulate  with  the  malar 


THE   SKELETON.  37 

bone ;  and  the  orbital  plate,  which  is  the  roof  of  the  malar 
process,  forming  a  partial  floor  to  the  orbital  cavity.  The 
large  foramen  leading  from  the  orbital  cavity  through  the 
orbital  plate  is  the  infraorbital  foramen  for  the  passage  of 
the  infraorbital  branch  of  the  superior  maxillary  branch  of 
the  fifth  nerve. 

The  palatine  bone  with  its  fellow  helps  to  form  the  roof 
of  the  oral  cavity  and  the  floor  of  the  nasal  cavity.  It  is 
composed  of  two  plates :  one,  vertical,  forming  the  lateral 
walls  of  the  posterior  nares  and  the  cranial  part  of  the 
walls  of  the  median  pterygoid  fossa,  and  a  portion  of  the 
nasal  wall  of  the  orbital  cavity ;  the  other,  horizontal,  form- 
ing part  of  the  roof  of  the  mouth.  The  vertical  plate 
is  pierced  by  two  foramina,  the  posterior  palatine  and  the 
spheno palatine,  each  of  which  transmits  a  palatine  nerve 
and  artery  (Fig.  16). 

The  vomer  is  a  single  narrow  bone  which  in  the  nasal 
cavity  articulates  dorsally  with  the  mesethmoid  and  ven- 
trally  with  the  palatines  and  the  palatine  plates  of  the 
maxillary,  in  the  median  line.  This  bone,  with  the  mes- 
ethmoid and  its  cartilage,  forms  the  nasal  septum,  dividing 
the  nasal  cavity  into  two  chambers.  It  is  best  demonstrated 
by  removing  the  palatines,  when  it  may  be  seen  extending 
craniad  from  its  bifurcated  articulation  with  the  presphe- 
noid  to  its  articulation  with  the  premaxillaries.  The  caudal 
portion  of  the  bone  is  expanded  horizontally  and  articu- 
lates with  the  ventral  ethmoturbinals.  Its  dorsal  margin 
is  bifurcated  for  articulation  with  the  mesethmoid. 

The  maxilloturbinal  is  a  paired  bone  occupying  the  an- 
terior portion  of  the  nasal  cavity  (Fig.  18).  It  is  composed 
of  a  few  scrolls  which,  when  the  nasal  bone  is  removed, 
may  be  seen  attached  to  the  maxillary.  It  consists  of  a 
horizontal  longitudinal  plate,  whose  lateral  border  is  fixed 
to  the  maxillary  while  the  medial  border  bifurcates  into  a 


3$  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

dorsal  curved  plate  and  a  ventral  scroll.  The  space  between 
the  maxilloturbinal  and  cranial  portion  of  the  lateral  eth- 
moid is  the  middle  nasal  meatus.  The  maxilloturbinal  bone 
in  man  receives  the  name  of  the  inferior  turbinated,  in  dis- 
tinction to  the  middle  and  superior  turbinated  bones,  con- 
stituting the  lateral  ethmoid. 

The  nasal  bone,  joining  with  its  fellow  in  the  median 
line,  forms  a  large  part  of  the  roof  of  the  nasal  chamber. 
It  articulates  with  the  premaxillary,  maxillary,  and  frontal 
on  the  surface,  and  the  ethmoid  within  the  nasal  chamber. 

The  lachrymal  bones  are  two  in  number  and  lie  in  the 
cranial  part  of  the  nasal  walls  of  the  orbits.  Each  articu- 
lates with  the  maxillary,  frontal,  os  planum  of  the  ethmoid, 
and  the  malar.  The  bone  has  about  half  of  the  area  of  the 
finger-nail.  The  lachrymal  canal  is  bounded  by  the  lachry- 


FIG.  19.     MEDIAL  OR  INNER  ASPECT  OF  THE  MANDIBLE. 
ang,  Angle;  cndyl,  condyle;  cor.  pr,  coronoid  process;  can,  canine  tooth ; 
inc,  incisor  teeth;  inf.  d.  fm,  inferior  dental  foramen;  in,  inferior 
notch;  mol,  molar  tooth;  prm,  premolar  teeth;  dt,  diastema;  sm, 
surface  of  symphysis ;  up,  superior  notch. 

mal  and  the  maxilla.  This  canal,  beginning  in  a  vertical 
groove,  the  lachrymal  groove,  carries  the  duct  permitting 
the  tears  to  pass  from  the  eye  into  the  nasal  chamber  (Fig. 
16). 


THE   SKELETON. 


39 


The  malar  bone  is  paired.  It  forms  the  cheek  as  well 
as  the  lateral  and  cranial  border  of  the  orbit.  The  arch 
largely  formed  by  this  bone  is  the  zygoma.  The  process 
projecting  dorsad  toward  the  postorbital  process  of  the 
frontal  bone  is  the  postorbital  process  of  the  malar.  The 
masseter  muscle  originates  on  the  border  of  the  malar. 

The  mandible  or  inferior  max- 
illary is  the  single  bone  forming 
the  lower  jaw  (Figs.  19  and 
2 1 ) .  It  is  made  up  of  two  halves 
which  are  united  by  an  immov- 
able articulation  or  symphysis  at 
the  chin.  Each  half  consists  of 
a  horizontal  and  an  ascending 
ramus.  On  its  alveolar  border 
the  horizontal  ramus  bears  three 
incisor  teeth,  a  canine,  two  pre- 
molars  and  a  molar  tooth.  In 
the  caudal  part  of  the  medial  sur- 
face of  this  ramus  is  the  inferior 
dental  foramen,  which  transmits 
the  inferior  dental  nerve  and 
artery  traversing  the  dental  canal 
extending  within  the  bone  to 
the  mental  foramen  on  the  lat- 
eral surface  near  the  base  of  the 
canine  tooth.  The  space  on  the 
dorsal  border  between  the  canine 
and  the  first  premolar  tooth  is 
called  the  diastema. 

The  ascending  ramus  or  por- 
tion of  the  bone  caudad  of  the 
inferior  tooth  is  marked  by  six  features:  (i)  the  fossa  on 
the  outer  or  lateral  surface  which  gives  insertion  to  the 


FIG.  20.  VENTRAL  ASPECT 
OF  LARYNX,  HYOID  BONES, 
AND  TONGUE.  The  tongue 
has  been  cut  transversely 
near  its  middle  and  its 
muscles  fixing  it  to  the 
hyoid  have  been  removed. 

bh,  Basihyal ;  ch,  ceratohyal ; 
cr,  cricoid  cartilage  of  the 
larynx ;  eh,  epihyal ;  ep, 
epiglottis ;  lg,  cricothyroid 
ligament ;  lyh,  thyrohyal ; 
rg,  rings  of  cartilage  in 
the  trachea;  tc,  thyroid 
cartilage  of  the  larynx; 
tm,  tympanohyal ;  sh, 
stylohyal. 


4°  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

masseter  muscle;  (2)  the  angle  which  is  the  caudo ventral 
termination  of  the  bone;  (3)  the  inferior  notch  imme- 
diately dorsal  of  the  angle;  (4)  the  condyle  for  the  articu- 
lation with  the  glenoid  cavity  of  the  temporal;  (5)  the 
superior  notch  dorsal  of  the  condyle;  (6)  the  coronoid 
process,  which  is  the  dorsal  termination  of  the  ascending 
ramus  and  gives  insertion  to  the  temporal  muscle. 

THE  HYOID  BONES  OR  HYOID  APPARATUS. 

The  hyoid  bones  consist  of  two  jointed  rods,  one  on 
either  side  (Figs.  20  and  21),  hanging  from  the  temporal 
bone,  and  supporting  the  larynx.  Each  rod  is  composed  of 
six  parts :  the  epihyal;  the  ceratohyal;  the  tympanohyal;  the 
basihyal;  and  the  thyrohyal.  The  dorsal  end  of  the  thyro- 
hyal  is  prolonged  by  a  piece  of  cartilage,  the  chondrohyal. 

The  hyoid  apparatus  varies  greatly  among  mammals. 
In  man  it  consists  of  a  single  bone  composed  of  the  body 
or  basihyal,  two  small  cornua  representing  the  ceratohyals, 
and  two  large  cornua  representing  the  thyrohyals.  The 
bone  is  suspended  from  the  skull  by  ligaments  correspond- 
ing to  the  bony  chain  in  the  cat. 

'PRACTICAL    QUESTIONS   AND   SUGGESTIONS. 

1.  How  many  more  bones  are  present  in  the  cat  than  in  man? 

2.  In  what  two  parts  of  the  skeleton  does  the  number  of  bones  in 
the  cat  exceed  those  in  man? 

3.  What  is  a  sesamoid  bone? 

4.  Find  on  a  specimen  a  sesamoid  bone  and  describe  it. 
/5.  Draw  a  lateral  aspect  of  the  skull  and  label  all  parts. 

6.  What  are  the  paired  bones  of  the  cranium? 

7.  Name  the  single  bones  of  the  face. 

*^.  Draw  the  caudal  aspect  of  the  skull  and  label  all  parts. 
9.  Which  bones  of  the  skull  derive  their  names  from  their  location? 

10.  Which  bones  of  the  skull  are  pierced  by  more  than  two  foramina? 

11.  Write  a  description  of  the  orbital  cavity. 

12.  Which  foramina  of  the  skull  derive  their  names  from  their  shape 
or  size? 


HOOPER 


THE   SKELETON.  41 

13.  Which  foramina  derive  their  names  from  their  location? 

14.  Which    foramina    transmit    important    blood-vessels? 

15.  Draw  figures  representing  relative  shapes  and  sizes  of  all  foram- 
ina of  the  skull. 

16.  What  bones  enter  into  the  formation  of  the  brain  cavity? 

17.  Write  about  200  words  describing  the  nasal  cavity. 

18.  Draw  a  ventro-lateral  aspect  of  the  auditory  bulla  and  label  all 
features. 

19.  Write  a  description  of  the  auditory  bulla  and  name  some  mam- 
mals in  which  it  is  absent. 

20.  Which  bones  of  the  skull  are  composed  of  more  parts  in  the 
young  than  in  the  adult? 

21.  Name  the  principal  sutures  of  the  skull. 

22.  Name  the  parts  of  the  sphenoid  bone  in  the  order  of  size. 

23.  Name  the  bones  of  the  skull  visible  from  the  dorsal  aspect. 

24.  Name  the  bones  of  the  skull  visible  from  the  cranial  aspect. 

25.  What  bone  of  the  cranium  paired  in  the  cat  is  single  in  man? 

26.  What  bone  present  in  face  of  the  cat  is  wanting  as  a  separate  ele- 
ment in  man? 

If  2.7.  Draw  lateral  aspect  of  mandible  and  label  all  features. 

28.  Name  the  bones  bearing  the  teeth. 

29.  Name  the  elements  of  hyoid  apparatus  in  order. 

30.  Draw  a  section  of  the  frontal  bone  showing  diploe. 

31.  Describe   the   difference   between   the    relative   locations   of   the 
cranial  and  facial  portions  of  the  skull  in  cat  and  man. 

32.  Name  five  membrane  bones  and  five  cartilage  bones. 

VERTEBRA. 

The  vertebral  column  is  composed  of  the  following  five 
groups  of  vertebrae  :  seven  cervical,  thirteen  thoracic,  seven 
lumbar,  three  sacral,  and  caudal  varying  from  four  to 
twenty-six.  The  following  six  features  are  common  to  all 
of  the  vertebrae  in  the  first  four  groups  except  the  atlas  : 
(i)  the  body  of  the  vertebra  (Fig.  22),  which  forms  the 
floor  of  the  neural  canal  and  articulates  with  the  adjacent 
vertebrae  by  means  of  interposed  discs  of  cartilage;  (2)  the 
transverse  processes,  which  project  laterad  from  the  body 
or  from  the  walls  of  the  neural  canal  ;  (3)  a  spinous  process, 
which  projects  dorsad  from  the  roof  of  the  neural  canal; 
5 


42  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

(4)  the  neural  arch,  composed  of  a  pedicle  on  either  side, 
forming  the  ventrolateral  walls  of  the  neural  canal,  and  the 


lamina,  extending  dorsad  from  the  pedicles  to  complete  the 
dorsal  wall  of  the  neural  canal;  (5)  the  intervertebral  notch, 
which,  with  the  notch  of  the  succeeding  vertebra,  forms  the 


THE   SKELETON.  43 


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44 


ELEMENTS    OF   MAMMALIAN    ANATOMY. 


intervertebral  foramen  for  the  exit  of  a  spinal  nerve;  (6) 
the  articular  processes,  two  of  which  project  craniad  and 
two  caudad  from  each  vertebra. 
The  former  are  called  the  anterior 
articular  processes  and  the  latter 
posterior  articular  processes. 

The  first .  cervical  vertebra,  or 
atlas,  is  characterized  by  its  large 
horizontally  expanded  transverse 
processes,  the  absence  of  a  spinous 
FIG.  22.  PLAN  OF  A  VER-  process,  and  its  rudimentary  body. 
Its  true  body  in  the  embryo  becomes 

sp,  Spinous  process ;  ar,  J  J 

articular  process;   ns,     united  to  the  axis  as  the  odontoid 
transverse  process ;  nc,  <-™  -   •>  r  ,  i 

neural  canal;  pd,  pedi-     process.     The  cranial  margin  of  the 
cle;    Im,   lamina;    en,     neural    arch    is    prolonged    at    each 

centrum   or   body.  . 

side   into  a  process   or  articulation 

with  the  occipital  condyles  (Fig.  17)  of  the  skull.  The 
root  of  this  articular  process  is  pierced  by  a  foramen  giving 
passage  to  the  first  spinal  nerve 
and  the  vertebral  artery  and  vein 
(Fig.  23,  fr).  From  the  lateral 
opening  of  this  foramen  (fr)  a 
groove  is  continued  ventrad  to 
the  middle  of  the  transverse  proc- 
ess, where  it  leads  into  the  trans- 
verse foramen  common  to  the 
first  six  cervical  vertebrae.  The 
vertebral  artery  and  vein  course 
through  this  canal  (Fig.  23). 

The  axis,  or  second  vertebra, 
is   characterized   by   its   odontoid 
process,  which  projects  within  the 
atlas,  and  also  by  its  elongated  spinous  process,  which  pro- 
jects both  craniad  and  caudad.     The  transverse  process  pro- 


23.       DORSOCAUDAL    As- 

PECT  OF  ATLAS. 

tr,  Transverse  process ;  nc, 
neural  canal;  sp,  spinous 
process;  fr,  aperture  of 
the  transverse  foramen 
which  enters  the  atlas  at 
vf\  azg,  anterior  artic- 
ular process ;  zg,  poster- 
ior articular  process. 


THE   SKELETON. 


45 


jects  caudad  from  the  body,  which  is  flattened  dorsoventrally. 


FIG.  24.     LATERAL  ASPECT  OF  THE  Axis. 

ar.  st,  Anterior  articular  process;  od.  pr,  odontoid  process ;  «/.  sp,  neural 
spine  or  spinous  process ;  p.  zg,  posterior  articular  process ;  trs.  pr, 
transverse  process;  vrt.  c,  transverse  foramen. 

This  process  is  pierced  at  its  base  by  the  transverse  foramen. 

The  remaining  five  cervicals 
are  very  similar  to  one  another. 
The  seventh  has  no  transverse 
foramen.  The  spinous  processes 
grow  successively  longer  from 
the  third  to  the  seventh  (Fig.  21). 
The  transverse  processes  of  the 
fourth  and  fifth  are  bifurcated, 
the  dorsal  branch  being  called 
the  transverse  clement  and  the 
ventral  one  the  costal  element, 
since  it  is  really  the  rudiment  of 
a  rib.  The  transverse  process  of 
the  fifth  ends  in  three  branches. 
The  following  features  are  com- 
mon to  all  thirteen  thoracic  ver- 
tebrae :  a  spinous  process,  pro- 
jecting from  the  dorsum  of  the 
neural  arch;  two  cranial  articular  processes,  facing  dorsad 
or  dorsolaterad ;  two  caudal  articular  processes,  facing  ven- 


ce 


FIG.  25.  LATEROCAUDAL  AS- 
PECT OF  THE  SECOND 
THORACIC  VERTEBRA. 

tr,  Transverse  process;  nc, 
neural  canal ;  ce,  facet  for 
tubercle  of  rib;  ar,  pos- 
terior articular  process ; 
s,  spinous  process ;  c, 
centrum ;  n,  interverte- 
bral  notch ;  e,  pedicle ;  /, 
lamina. 


46  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

trad  or  ventromediad ;  a  body  whose  transverse  diameter  is 
greater  than  the  vertical  diameter ;  and  transverse  processes. 
There  are  two  half  facets  on  each  side  of  the  body  of  every 
thoracic  vertebra  except  the  first,  eleventh,  twelfth,  and 
thirteenth.  The  head  of  a  rib  thus  articulates  with  two 
vertebrae  (Fig.  28).  The  body  of  the  first  vertebra  bears 
on  each  side  a  whole  facet  and  a  half  facet.  The  eleventh, 
twelfth,  and  thirteenth  bear  a  whole  facet  on  each  side  of 
the  body. 

The  transverse  processes  of  the  first  eleven  bear  facets 
for  the  articulation  with  the  tubercles  (Fig.  25)  of  the 
ribs.  The  last  three  thoracic  vertebrae  are  characterized  by 
•mammillary  processes  springing  from  the  dorsolateral  por- 
tion of  the  roots  of  the  anterior  processes. 

The  following  features  are  common  to  all  of  the  lumbar 
vertebra:  a  spinous  process  projecting  dorsocraniad  (Fig. 
26)  ;  a  transverse  process  projecting  ventrocraniad  on  either 
side  from  the  body;  anterior  articular  processes  and  poste- 
rior articular  processes.  A  mammillary  process  is  present 
on  the  root  of  the  anterior  articular  process  of  the  first  five 
bones,  and  an  accessory  process  occurs  on  the  caudal  margin 
of  the  wall  of  the  neural  arch  of  all  except  the  last  vertebra. 
The  transverse  processes  increase  in  length  and  curvature 
caudally.  The  spinous  processes  increase  in  length  in  the 
same  order,  and  the  neural  canal  likewise  enlarges  caudally. 

The  sacrum  is  a  single  bone  (Fig.  27)  formed  by  the 
union  of  three  sacral  vertebras.  The  limit  of  each  element 
is  marked  by  the  dorsal  and  ventral  intervertebral  foramina 
which  furnish  passage  for  the  dorsal  and  ventral  branches 
of  the  spinal  nerves.  The  two  tubercles  on  either  side  of 
each  of  the  three  median  spinous  processes  are  the  result 
of  the  fusion  of  the  articular  processes.  The  cranial  por- 
tion of  the  bone  presents  on  its  lateral  aspect  the  auricular 


THE   SKELETON. 


47 


surfaces  for  articulation  with  the  ilium.  This  expansion 
appears  to  be  a  modified  transverse  process.  Prominent 
transverse  processes  also  project  from  the  caudal  angles. 

The  caudal  vertebrae  vary  greatly  in  number.  Accord- 
ing to  Mivart,  there  are  only  four  in  the  Manx  cat;  and 
according  to  Jayne,  there  may  be  as  many  as  twenty-six  in 
some  varieties  of  the  common  cat.  The  transverse  processes 


FIG.  26.  CAUDAL  ASPECT  OF 
FOURTH  LUMBAR  VERTEBRA. 

a,  Accessory  process ;  cr,  centrum 
or  body ;  pa,  pedicle ;  tr,  trans- 
verse process;  s,  neural,  canal ; 
sp,  spinotis  process ;  zg,  the 
mammillary  process  of  the  an- 
terior articular  process ;  am, 
lamina ;  pz,  articular  process. 


FIG.  27.  DORSAL  ASPECT  OF  THE 
SACRUM. 

fl,  Floor  of  the  neural  canal;  fr, 
dorsal  aperture  of  the  inter- 
vertebral  foramen ;  It,  lateral 
mass ;  pzg,  posterior  articular 
process ;  sp,  spinous  process ;  si, 
auricular  surface  for  articula- 
tion with  the  ilium;  tr,  trans- 
verse process;  zgt,  tubercle 
formed  by  fusion  of  the  artic- 
ular processes;  sg,  anterior 
articular  processes. 


and  articular  processes  become  less  prominent  from  the 
third  vertebra  to  the  eighth  or  ninth,  where  they  are. present 
only  as  slight  ridges.  The  spinous  process  is  present  in  the 
first  three,  but  dwindles  to  a  ridge  in  the  fourth.  The  first 
six  or  seven  elements  possess  a  neural  arch  which  more 
distally  loses  its  roof,  making  the  neural  canal  a  mere 


48  ELEMENTS    OF   MAMMALIAN    ANATOMY. 

groove.  The  groove  becomes  fainter  distally  and  finally 
disappears  entirely.  The  chevron  bones  are  the  paired 
ossicles  projecting  ventrad  from  the  cranial  ends  of  the 
bodies  of  the  vertebrae,  from  the  second  or  third  to  the 
thirteenth  vertebra.  In  the  sixth,  seventh,  and  eighth  ver- 
tebrae the  chevron  bones  unite  ventrally  in  the  middle  line, 
forming  an  arch.  The  last  ten  caudal  vertebrae  are  scarcely 
more  than  cylinders  of  bone  representing  the  bodies  of  the 
vertebrae. 

The  number  of  vertebrae  in  the  different  species  of  mam- 
mals varies  widely.  As  a  rule,  there  are  seven  elements  in 
the  cervical  region.  The  sea  cow  (Manatus)  has  only  six 
cervical  vertebrae,  while  the  three-toed  sloth  has  nine.  The 
number  of  thoracico-lumbar  varies  from  sixteen  in  the 
orang  to  thirty-six  in  the  cetacean  Delphinus.  The  ele- 
ments composing  the  sacrum  likewise  vary  from  one  in  the 
ape,  Cercopithecus,  to  nine  in  some  of  the  Edentata.  The 
human  sacrum  is  composed  of  from  four  to  six  vertebrae. 
The  same  is  true  of  the  gorilla,  chimpanzee,  and  orang. 
The  caudal  vertebrae  vary  greatly  in  number  in  the  different 
forms.  In  the  adult  human  there  are  present  only  four  or 
five  vertebrae,  which  form  a  single  bone,  the  coccyx,  while 
in  the  embryo  eight  segments  make  up  the  caudal  region. 
Ossification  takes  place,  however,  in  only  five  or  six 
segments. 

THE  STERNUM. 

The  sternum  of  the  cat  is  composed  of  eight  pieces, 
called  sternebrce,  which  lie  in  the  median  line  on  the  ven- 
tral side  of  the  chest  (Fig.  21).  The  sternum  serves  for 
the  attachment  of  the  cartilaginous  portions  of  nine  pairs 
of  ribs.  The  first  sternebra  (Fig.  28),  which  ends  craniad 
in  a  laterally  compressed  pointed  process,  is  the  manu- 
briurn.  The  six  succeeding  sternebrae  form  the  body  or 


THE   SKELETON. 


49 


gladiolus;  the  caudal  piece  is  called  the  ensiform  or  xi- 
phoid process.  It  is  terminated  by  a  flat  piece  of  cartilage. 
The  cartilaginous  portion  of  the  first  rib  articulates  witE 
the  manubrium  near  its  middle.  The  ribs  from  the  second 


I 

n 


FIG.  28.  VENTRAL  ASPECT  OF  THE  BONES  OF  THE  THORAX.  The  numbers 
on  the  vertebral  or  bony  portions  of  the  ribs  indicate  the  names  of 
the  ribs.  The  numbers  of  the  last  four  ribs  are  placed  just  craniad 
of  them. 

c,  Cartilaginous  part  of  the  first  rib ;  cr,  cartilaginous  disc  between  the 
bodies  of  the  vertebrae ;  en,  ensiform  process ;  h&,  heads  or  capitula 
of  ribs;  m,  manubrium,  mr,  attachment  of  twelfth  to  the  eleventh 
rib;  n,  free  termination  of  thirteenth  rib;  r,  attachment  of  the 
eleventh  to  the  tenth  rib;  tb,  tubercle  of  first  rib;  in,  transverse 
process  of  first  thoracic  vertebra;  v,  body  of  vertebra. 

6 


ELEMENTS   OF   MAMMALIAN   ANATOMY. 


to  the  seventh  inclusive  are  attached  at  the  junctions  of  the 
sternebrse.  The  eighth  and  ninth  ribs  are  attached  near 
together  on  the  caudal  end  of  the  seventh  sternebra. 

RIBS. 

There  are  thirteen  pairs  of  ribs  in  the  cat.  The  nine 
cranial  are  called  true  ribs  because  they  articulate  dorsally 
with  the  spinal  column  and  ventrally  with  the  sternum. 
The  other  four  (Fig.  28)  are  false 
ribs,  three  of  which  articulate  ventrally 
with  other  ribs,  while  the  fourth  has 
no  ventral  articulation,  and  is  there- 
fore called  a  floating  rib.  Each  rib 
is  composed  of  two  parts,  the  vertebral 
or  bony  portion  and  the  sternal  or  car- 
tilaginous portion. 

The  following  description  of  the 
sixth  will  serve  to  give  a  correct  idea 
in  general  of  the  anatomy  of  a  rib.  Its 
vertebral  portion  (Fig.  29)  presents 
four  features:  a  head  or  capitulum, 
which  articulates  with  the  bodies  of 
the  fifth  and  sixth  thoracic  vertebrae ;  a 
tubercle,  which  articulates  with  the 
transverse  process  of  the  sixth  thoracic 
vertebra;  a  neck,  which  is  the  con- 
stricted portion  between  the  capitulum 
and  tubercle;  and  the  shaft,  including 
the  portion  of  the  rib  between  the 
tubercle  and  its  articulation  with  the  sternal  or  cartilaginous 
portion.  The  bend  in  the  shaft  beyond  the  tubercle  is  the 
angle.  The  sternal  portion  of  the  rib,  consisting  of  carti- 
lage, is  sometimes  called  the  costal  rib.  In  the  sixth  rib  the 
costal  portion  is  about  half  as  long  as  the  vertebral  portion. 


FIG.  29.  CAUDAL  AS- 
PECT OF  SIXTH  RIB. 

ag,  Angle;  cr,  pit  for 
articulation  with 
cartilaginous  p  o  r  - 
tion;  h,  capitulum; 
nk,  neck ;  sh,  shaft ; 
tb,  tubercle  with 
facet  for  articula- 
tion with  transverse 
process. 


THE   SKELETON.  51 

Certain  ribs  present  marked  features  varying  from  the 
sixth.  The  first  rib  is  stout  and  flat  and  has  no  distinct 
angle.  The  articular  surface  of  its  head  is  not  divided  into 
two  facets,  as  is  the  case  in  all  the  others  except  the  three 
caudal  ones.  The  lengths  of  the  ribs  increase  from  the  first 
to  the  ninth.  The  last  three  ribs  have  no  necks  and  no 
tubercles  for  articulation  with  the  transverse  processes  of 
the  vertebrae. 

The  number  of  ribs  varies  from  nine  pairs  in  the  cetacean 
Hyperoodon  to  twenty- four  in  the  two-toed  sloth  (Cho- 
loepus).  In  most  fishes  and  snakes,  ribs  are  present 
throughout  both  the  trunk  and  tail  regions,  but  with  the 
assumption  of  life  on  land,  and  the  development  of  limbs, 
the  vertebrates  have  suffered  a  degeneration  of  the  ribs  in 
all  parts  except  the  middle  portion  of  the  trunk.  In  the 
embryo,  however,  anlage  (beginning)  of  ribs  occurs  in  all 
regions  of  the  trunk,  but  they  early  coalesce  with  the  ver- 
tebrae except  in  the  thorax. 

PRACTICAL   QUESTIONS    AND    SUGGESTIONS. 

^(i.  Draw  caudal  aspect  of  third  thoracic  vertebra  and  label  all 
features. 

2.  Describe  the  differences  between  the  first  and  last  thoracic  ver- 
tebrae. 

3.  What  feature  common  to  all  thoracic  vertebrae  not  present  on 
any  of  the  other  vertebras? 

«/4.  Draw  the  caudal  aspect  of  the  fourth  cervical  vertebra. 

5.  What  feature  common  to  all  cervical  vertebrae  except  seventh 
but  not  present  in  any  other  vertebrae? 
p^  6.  Draw  cranial  aspect  of  atlas  and  label  all  features. 

7.  Compare  the  third  and  seventh  cervical  vertebrae. 

8.  What  two   features-  serve  to   distinguish  the  lumbar   from   all 
other  vertebrae? 

9.  Draw   the   cranial   aspect   of   the   second   lumbar   vertebra   and 
label  all  features. 

10.  Wherein  does  the  seventh  lumbar  vertebra  differ  from  the  first? 

11.  How  do  you  distinguish  the  caudal  from  the  cranial  aspect  of 
any  vertebra? 


52  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

i/12.  Draw  ventral  aspect  of  sacrum  and  label  all  features. 

13.  Give  the  two  features  distinguishing  the  caudal  vertebrae  from 
all  others. 

14.  Note  the  size  and  direction  of  the  spinous  process  throughout 
the  column. 

15.  Describe  the  variation  in  number  of  the  different  groups  of  ver- 
tebrae in  other  mammals. 

16.  Draw  lateral  aspect  of  sternum  and  label  all  features. 

17.  Describe  the  attachment  of  ribs  to  sternum. 

18.  What  features  common  to  all  the  ribs? 

19.  Name  ribs  having  a  tubercle. 

20.  Draw  first  rib  and  label  all  features. 

21.  Draw  cranial  aspect  of  ninth  rib  and  label  all  features. 

22.  How  do  you  distinguish  a  false  rib  from  a  true  rib? 

23.  What  features  mark  the  caudal  aspect  of  a  rib? 

^24.  Make   a   drawing   showing  the   articulation   of   a   rib  with  the 
spinal  column  and  label  all  parts. 

25.  How  do  ribs  vary  as  to  number  in  mammals? 

THE  THORACIC  LIMB. 

The  thoracic  or  fore-limb  of  the  cat  is  composed  of  a 
scapula,  clavicle,  humerus,  ulna,  radius,  seven  carpals,  five 
metacarpals,  and  fourteen  phalanges  (Fig.  21).  The  sca- 
pula and  clavicle  form  the  shoulder  girdle. 

The  scapula,  commonly  called  the  shoulder-blade  (Fig. 
30),  is  not  articulated  with  the  bones  of  the  trunk,  but  is 
held  in  position  by  the  serratus  magnus,  levator  anguli 
scapulae,  and  other  less  important  muscles.  It  articulates 
with  the  head  of  the  humerus  by  the  glenoid  cavity.  It 
presents  three  well-marked  borders :  the  cranial  or  anterior, 
the  vertebral,  and  the  axillary  adjacent  to  the  vertebrae  on 
the  side  near  the  axilla  or  armpit.  The  outer  surface  of  this 
bone  is  divided  by  a  strong  spine  into  two  nearly  equal 
fossae,  the  cranial  of  which  is  the  supraspinous,  and  the 
caudal  one  the  infraspinous,  fossa.  From  the  lower  part 
of  the  spine  project  the  acromion  and  metacromion  proc- 
esses. The  subscapular  fossa  occupies  the  entire  inner  or 
medial  surface. 


THE   SKELETON. 


53 


A  slight  constriction  between  the  base  of  the  spine  and 
the  margin  of  the  glenoid  cavity  is  termed  the  neck.    From, 


FIG.  30.    LATERAL  OR  OUTER  ASPECT  OF  THE  SCAPULA. 

ac,  Acromion  process;  ax,  axillary  border;  c,  coracoid  process;  gi, 
glenoid  cavity ;  m,  metacromion  process ;  sc,  suprascapular  notch ; 
sp,  spine ;  sup.  fos,  supraspinous  fossa ;  vr,  vertebral  border ;  n,  neck. 

the  cranial  side  of  the  latter  the  coracoid  process  curves 
mediad. 

The  clavicle  is  a  slender 
curved  bone,  about  one  inch 
long,  imbedded  in  the  mus- 
cle between  the  manubrium  FlG.  3I._CAUDAL  ASPECT  OF  LEFT 

CLAVICLE. 


b,  Medial  end ;  a,  lateral  end. 


and     the     coracoid     process 
(Fig.  21 ).     It  does  not  ar- 
ticulate with  any  bone,  but  is  held  in  place  by  the  cephalo- 
humeral  and  cleidomastoid  muscles  (Fig.  48). 

The  shoulder  girdle  varies  somewhat  among  the  Mam- 
malia. The  clavicle  is  never  fully  developed  in  any  of  the 
Carnivora.  Primates,  Chiroptera,  Edentata,  and  Monotre- 
mata  are  the  only  orders  in  which  all  the  species  possess 
clavicles.  A  third  element  of  the  shoulder  girdle,  known  as 
the  coracoid,  is  a  fully  developed  bone  only  in  the  Monotre- 


54 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


mata,  where  it  articulates  at  one  end  with  the  scapula, 
forming  part  of  the  glenoid  cavity,  and  at  the  other  end 
with  the  presternum.  In  the  other 
mammals  the  coracoid  is  represented 
by  the  coracoid  process  of  the  scapula, 
which  ossifies  from  a  separate  center. 
In  many  of  the  lower  vertebrates  a  dis- 
tinct coracoid  is  present. 

The  humerus  is  the  bone  of  the 
arm  or  brachium.  It  articulates  prox- 
imally  with  the  glenoid  cavity  of  the 
scapula  (Fig.  21)  and  distally  with 
the  ulna  and  radius.  It  consists  of 
three  parts :  the  proximal  extremity 
bearing  the  head,  the  middle  portion 
or  shaft,  and  the  distal  extremity  (Fig. 
32).  The  greater  and  lesser  tubcr- 
osities  separated  by  the  bicipital  groove 
lodging  the  tendon  of  the  biceps  'mus- 
cle, are  the  two  processes  on  the  proxi- 
mal extremity.  The  former  is  the 
larger  and  more  craniad  and  serves  for 
the  insertion  of  the  supraspinatus  mus- 
cle (Fig.  49).  The  distal  extremity  is 
marked  by  two  important  projections, 
the  external  and  internal  condyles. 
Extending  proximad  from  the  external 
condyle  is  the  supinator  ridge.  Proxi- 
mad of  the  internal  condyle  is  the 
supracondyloid  foramen  transmitting 


FIG.  32.  CRANIAL  AS- 
PECT OF  RIGHT  HU- 
MERUS. 

bl,  Bicipital  groove ; 
cr,  supracondyloid 
ridge ;  cp,  capitel- 
lum  for  articulation 
with  the  radius ;  dr, 
deltoid  ridge ;  et, 
external  condyle ; 
gt,  greater ^  tuber- 
osity ;  it,  internal 
condyle ;  It,  lesser 
tuberosity;  sp,  su- 
pracondyloid fora- 
men or  entepicon- 


suypinatforrarTdgne;;  £     the  median  nervp.  and  brachial  artery 
(Figs.    $»  and  -89).      The   olecranon 
fossa  is  the  deep  cavity  on  the  caudal 
aspect  of  the  bone,  opposite  the  coronoid  fossa.    The  articu- 


trochlea    for    artic- 
ulation with  ulna. 


THE   SKELETON. 


55 


lar  surface  of  the  distal  extremity  consists  of  the  capitellum, 
for  articulation  with  the  head  of  the  radius,  and  the  trochleor 
for  articulation  with  the  sigmoid  cavity 
of  the  ulna.     On  the  cranial  side  of  the 
proximal  third  of  the  bone  is  the  rough 
deltoid   ridge    for   the    insertion    of   the 
deltoid    muscle    which    arises    from    the 
shoulder  girdle. 

The  ulna  is  the  longest  bone  of  the 
forearm  or  antebrachium,  and  is  caudad 
of  the  radius.  It  articulates  in  the  greater 
sigmoid  cavity  with  the  trochlea  of  the 
humerus  and  in  the  lesser  sigmoid  cavity 
with  the  head  of  the  radius.  The  distal 
articulation  is  with  the  radius,  cuneiform 
and  pisiform  (Fig.  21).  The  olecranon 
process  forms  the  proximal  termination 
of  the  bone  and  serves  for  the  insertion 
of  the  triceps  muscle.  Distad  of  the  sig- 
moid cavity  is  a  projection  known  as  the 
coronoid  process.  The  styloid  process 
forms  a  small  projection  on  the  distal 
extremity  of  the  bone. 

The  radius  is  the  preaxial  or  cranial 
bone  of  the  antebrachium.  It  articulates 
proximally  with  the  capitellum  of  the 
humerus  and  the  lesser  sigmoid  cavity 
of  the  ulna,  and  distally  with  the  scapho- 
lunar  and  ulna.  It  bears  but  two  proc- 
esses, the  tubercle  and  the  styloid  process. 
The  tubercle  (Fig.  34)  is  a  slight  knot 
near  the  proximal  end  on  the  ulnar  side. 
Proximal  from  the  tubercle  is  the  neck  which  supports  the 
head  bearing  a  concave  crown  for  articulation  with  the 


FIG.  33.  LATERAL 
OR  OUTER  AS- 
PECT OF  THE 
RIGHT  ULNA. 

ar,  Articular  facet 
for  radius ;  cr, 
coronoid  proc- 
ess ;  gs,  greater 
sigmoid  cavity ; 
Is,  lesser  sigmoid 
cavity;  on,  ole- 
cranon process ; 
st,  styloid  proc- 
ess. 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


capitellum  of  the  humerus.  The  styloid  process  projects 
from  the  distal  end  parallel  with  the  process  of  the  same 
name  on  the  ulna. 

The    bones    of    the    antebrachium    in 

£r 

many  mammals  are  more  or  less  coal- 
esced. In  the  Chiroptera  and  many  of  the 
Ungulates  the  radius  is  enlarged  at  the 
expense  of  the  ulna,  whose  proximal  third 
only  remains.  The  primitive  Ungulates 
of  the  lower  tertiary  period  possessed  a 
complete  ulna  as  well  as  radius.  The 
phylogeny  of  the  horse's  limb  illustrates 
the  gradual  development  of  the  ante- 
brachium of  the  Equidse  (Fig.  35). 
Fossil  remains  reveal  the  fact  that  mam- 
mals existed  as  early  as  the  triassic 
period,  when  the  sedimentary  rock  form- 
ing the  triassic  strata  was  laid  down. 
This  probably  occurred  10,000,000  years 
ago. 

According   to   palaeontological   investi- 


FIG.    34.      MEDIAL 
OR     INNER    AS- 
PECT  OF    RIGHT     gations,    the   Ungulata   arose    from    the 
RADIUS.  ~ 

t  ondylarthra ,  a  group  of  small  five-toed 


mammals  of  the  lower  Eocene,  best  repre- 


fc,  Articulatory 
surface  for  capi- 
tellum  of  hu- 
merus;  hd,  head  sented  by  the  typical  genus  Phenacodus. 

In  this  genus  and  its  successor,  Hyraco- 
theriwn,  the  ulna  and  radius  are  well 
developed  and  distinct.  Orohippus,  the 
descendant  of  Hyracotherium,  also  shows 
a  distinct  radius  and  ulna,  but  in  the  later 
forms  of  the  horse  line  the  ulna  gradually 
diminishes  in  size  and  becomes  more  and 
more  coalesced  with  the  radius,  until  in 

Equus    scarcely    more    than    the    proximal    third    remains 

(Fig.  37)- 


— the  point  of 
the  arrow  is  on 
the  articulating 
surface  for  the 
lesser  sigmoid 
cavity;  nk,  neck; 
sc,  articulatory 
surface  for 
scapholunar ;  st, 
styloid  process ; 
tb,  tubercle;  ul, 
facet  for  ulna. 


THE   SKELETON. 


57 


Carpus. — The  carpus  consists  of  seven  bones  arranged 
in  two  rows  (Fig.  36).  Beginning  on  the  pollex  side,  the 
scapholunar,  cuneiform,  and  pisiform  compose  the  proxi- 


A   Z 


«g* 

FIG.  35.     (See  next  page  for  explanation.} 

mal  row,  and  the  trapezium,  trapezoid,  magnum,  and  unci- 
form  form  the  distal  row.  The  scapholunar,  easily  dis- 
tinguished because  of  its  large  size,  articulates  with  the 


58  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

radius,  cuneiform,  unciform,  magnum,  trapezoid,  and  tra- 
pezium. The  cuneiform  articulates  with  the  ulna,  unci- 
form, pisiform,  and  scapholunar.  The  pisiform  is  next  to 
the  scapholunar  in  size.  It  projects  prominently  laterad 


\JJ 


FIG.  35.    GENEALOGY  OF  THE  HORSE. 

F,  Forefoot;  H,  hindfoot;  A,  forearm;  L,  leg;  I,  Orohippus;  //, 
Mesohippus;  III,  Miohippus;  IV,  Protohippus;  V,  Pliohippus;  VI, 
Equus;  2,  3,  4,  and  5  are  the  second,  third,  fourth,  and  fifth  digits 
respectively;  me,  metacarpus;  mi,  metatarsus;  p,  phalanges;  u, 
ulna;  r,  radius;  t,  tibia;  f,  fibula. —  (After  Marsh.) 


THE   SKELETON. 


59 


from   the   cuneiform   and   articulates   with   the   ulna   and 
cuneiform.     The   trapezium   is   the   smallest   bone   of   the 

carpus.  It  is  crescentic  in 
shape  and  articulates  with 
the  scapholunar,  trapezoid, 
and  first  and  second  meta- 
carpals.  The  trapezoid  is 
almost  as  small  as  the  trape- 
zium. It  is  distinguished  by 
its  flatness.  It  articulates 
with  the  scapholunar,  mag- 


A.  B. 

FIG.  36. 

A,  Dorsal  aspect  of  left  manus  of  cat:  a,  First  phalanx  of  the  pollex;  b, 

second  or  terminal  phalanx;  en,  cuneiform;  h,  head  of  fourth  meta- 
carpal;  m,  magnum;  mt,  metacarpal  4;  n,  claw;  pi,  pisiform;  s, 
sesamoid  bone;  st,  scapholunar;  td,  trapezoid;  tm,  trapezium;  u, 
unciform;  i,  2,  and  3,  first,  second,  and  third  phalanges  of  the 
middle  digit. 

B,  Generalized  type  of  carpus  as  found  in  lower  vertebrates  :  c,  Centrale  ; 

if  intermedium  or  lunare;  r,  radiale  or  scaphoid;  ra,  radius;  m, 
metacarpals;  u,  ulnare  or  cuneiform;  ul,  ulna;  I,  carpalia  I,  or 
trapezium;  2,  carpalia  2,  or  trapezoid;  3,  carpalia  3,  or  magnum; 
4  and  5,  carpalia  4  and  5,  or  unciform. 

num,  second  metacarpal,  and  trapezium.  This  bone  is  not 
visible  on  the  palmar  surface  of  the  wrist.  The  magnum 
articulates  with  the  scapholunar,  trapezoid,  unciform,  and 
second,  third,  and  fourth  metacarpals.  The  unciform  can 
be  recognized  by  its  wedge  shape.  It  articulates  with  the 
scapholunar,  cuneiform,  magnum,  and  fourth  and  fifth  meta- 
carpals. Each  carpal  bone  develops  from  a  single  center 
except  the  scapholunar,  which  develops  from  two  centers. 


6o 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


The   typical   arrangement   of    the   vertebrate    carpus    is 
shown  in  figure  36,  B.    The  pisiform  does  not  belong  to  the 
cartilaginous  skeleton,  but  is  a  sesa- 
moid   bone.     In   all   mammals   pos- 
**     $\      sessing   five   digits,    the    anlage    of 
/..</  ^  three   bones   in   the   proximal   row, 

five  bones  in  the  distal  row,  and  a 
central  element  occurs  in  the  embryo, 
but  through  fusion  of  elements  a 
less  number  is  present  in  most  adults. 
Thus,  in  the  cat  the  radiale  and  in- 
termedium and  centrale  unite  to  form 
the  scapholunar.  In  all  forms  car- 
palia  4  and  5  coalesce  to  form  the 
unciform. 

Metacarpus.  —  There  are  five 
metacarpal  bones  forming  the  middle 
region  of  the  forefoot.  They  are 
named,  beginning  on  the  pollex  side, 
first,  second,  third,  fourth,  and  fifth 
metacarpals  respectively.  Each  bone 
consists  of  a  proximal  extremity  or 
base,  a  middle  portion  or  shaft,  and 
a  distal  extremity  or  head  (Fig. 
36).  These  bones  are  curved  so  as 
to  be  slightly  convex  on  the  dorsal 
aspect. 

The  number  of  metacarpals  in 
mammals  varies  from  one  in  Equus 
to  five  which  are  present  in  most 
orders.  Nearly  all  the  species  of  every 
order,  except  the  Edentata  and  Un- 

gulata,  possess  five  metacarpals.     In  the  pig  and  hippopota- 
mus there  are  four  metacarpals,  in  the  rhinoceros  three,  and 


FIG.  37.  LATERAL  AS- 
PECT OF  LEFT  FORE- 
LIMB  OF  EQUUS. 

h,  Humerus ;  m$,  third 
metacarpal ;  mi,  fourth 
metacarpal ;  p,  phalan- 
ges ;  r,  radius ;  s,  sesa- 
moid;  sc,  scapula;  ua, 
ulna;  a,  scaphoid;  c, 
semilunar ;  m,  cunei- 
form;  n,  pisiform;  w, 
magnum;  u,  unciform. 


THE   SKELETON.  61 

in  the  camel,  deer,  sheep,  and  cow  two.  In  the  last  three 
forms  the  metacarpals  present  are  the  third  and  fourth, 
which  in  the  adult  are  coalesced  into  a  single  bone  known 
as  the  cannon-bone.  Remnants  of  the  second  and  fifth 
metacarpals  are  present  in  the  deer,  sheep,  and  cow,  as  the 
small  caudo-lateral  hoofs  indicate.  The  functional  meta- 
carpal  present  in  the  horse  is  the  third.  The  reduction  of 
metacarpals  in  the  ancestral  forms  of  the  horse  is  shown  in 
figure  35,  and  will  be  referred  to  again  in  the  description  of 
the  phalanges. 

Phalanges. — The  cat  has  five  toes  or  digits  on  the  fore- 
foot, called  pollex,  index,  medius,  annulus,  and  minimus. 
Each  digit,  except  the  pollex,  consists  of  three  phalanges 
(Fig.  36).  The  pollex  or  thumb  has  only  two  phalanges. 
The  row  of  phalanges  articulating  with  the  metacarpals 
is  called  the  proximal,  the  terminal  row  the  distal,  and 
the  remaining  row  the  middle  phalanges.  Two  small 
sesamoid  bones  are  attached  on  the  volar  side  of  the  junc- 
tion of  each  proximal  phalanx  with  the  metacarpal.  Each 
distal  phalanx  has  its  proximal  end  produced  caudal  on  the 
palmar  aspect  so  that  its  articular  surface  faces  dorsal.  The 
distal  phalanges  terminate  in  claws  which  are  retractile. 

The  number  of  digits  in  the  forefoot  of  Mammalia  varies 
from  one  to  five.  Nearly  all  the  species  of  every  order  ex- 
cept the  Edentata  and  Ungulata  possess  five  digits.  The 
tapir  has  four  functional  digits.  The  cow,  deer,  sheep,  and 
pig  also  have  four  digits,  but  only  two  are  functional,  the 
second  and  the  fifth  being  atrophied  and  terminating  in  the 
small  caudo-lateral  hoofs  which  do  not  touch  the  ground. 
The  rhinoceros  has  three  functional  digits,  and  the  Equidse 
possess  only  one  digit  (Fig.  37),  the  third,  though  the 
atrophied  remnants  of  the  second  and  fourth  metacarpals 
are  present  as  splint  bones  which  do  not  support  phalanges. 

As  before  stated,   the  Ungulates   are   undoubtedly   de- 


62  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

scendants  of  a  five- toed  ancestor  of  Eocene  times.  The 
evolution  of  the  horse's  limb  and  the  reduction  in  the  num- 
ber of  digits  are  shown  in  figure  35.  Fossil  remains  of 
the  ancestors  of  the  horse  have  been  found  in  western 
United  States,  Europe,  and  South  America.  Orohippus 
lived  in  the  region  of  Wyoming,  Montana,  and  Idaho  prob- 
ably more  than  5,000,000  years  ago,  when  that  country  was 
more  or  less  marshy,  and  it  was  necessary  that  the  mam- 
mals should  possess  a  spreading  foot  which  would  not  per- 
mit them  to  sink  too  deep  into  the  mud.  As  the  ground 
became  firmer  and  preying  Carnivora  more  numerous,  the 
foot  of  the  horse  adapted  itself  to  rapid  flight  over  solid 
ground.  Thus,  through  use  and  natural  selection  the  third 
digit  was  enlarged  at  the  expense  of  the  other  digits.  Con- 
firmation of  this  ancestral  history  of  the  horse  is  found  by 
an  examination  of  the  early  embryonic  stages.  According 
to  Ewart,  a  horse  embryo  35  cm.  long  possesses  quite  well- 
developed  second  and  fourth  metacarpals  terminating  with 
phalangeal  structures.  The  ulna  and  radius  of  an  embryo 
50  mm.  long  are  strikingly  similar  to  these  same  bones  in 
Mesohippus.  In  a  still  younger  embryo  the  ulna  is  com- 
plete and  correspondingly  as  large  as  in  Orohippus. 

As  to  the  method  of  walking,  mammals  are  spoken  of 
as  plantigrade,  digitigrade,  and  ungutigrade.  The  first 
mode  of  progression  is  exemplified  by  the  bear,  which  places 
its  metacarpals  and  phalanges  flat  on  the  ground  in  walk- 
ing. The  cat  is  digitigrade,  walking  on  its  toes.  The  horse 
and  cow  are  unguligrade,  as  they  walk  upon  the  hoof.  In 
some  cases,  as  in  the  Cetacea,  the  forefoot  is  adapted  for 
swimming  instead  of  walking,  and  the  number  of  phalanges 
to  each  digit  is  more  than  three. 

PRACTICAL   QUESTIONS    AND    SUGGESTIONS. 

1.  What  bones  compose  the  shoulder  girdle? 

2.  How  is  the  thoracic  limb  attached  to  the  trunk? 


THE   SKELETON.  63 

3.  What  does  the  condition  of  the  clavicle  in  the  cat  indicate  as  to 
its  past  history? 
4^-4.  Draw  the  medial  aspect  of  the  scapula  and  label  all  parts. 

5.  What  is  the  significance  of  the  coracoid  process? 

6.  Which  processes  of  the  scapula  derive  their  names  from  their 
location  and  which  from  their  shape? 

7.  How  do  you  distinguish  the  right  from  the  left  scapula? 

8.  Draw  the  caudal  aspect  of  the  humerus  and  label  all  features. 

9.  Describe  what  is  seen  in  looking  directly  at  the  distal  articulat- 
ing surfaces  of  the  humerus. 

10.  How  do  you  distinguish  the  right  from  the  left  humerus? 

11.  What  features  of  the  humerus  derive  their  names  from  their 
shape? 

xi2.  Draw   the   medial   or    inner  aspect   of    the   ulna   and   label    all 
features. 

13.  What  features  of  the  ulna  derive  their  names  from  their  form? 

14.  How  do  you  distinguish  the  right  from  the  left  ulna? 

15.  Describe  the  articulations  of  the  radius. 

x  16.  Draw  lateral  aspect  of  radius  and  label  all  features. 

17.  Describe  the  condition  of  the  bones  of  forearm  in  the  horse  and 
its  ancestors. 

18.  In  a  five-month  fetus  of  the  horse  the  ulna  is  distinct   from 
radius  and  complete,  while  in  the  mature  animal  but  little  more  than  the 
distal  third  remains,  and  is  anchylosed  to  the  radius.      Explain  sig- 
nificance of  this  fact. 

19.  Draw  ventral  aspect  of  carpus  and  label  all  parts. 

20.  Wherein  is  the  chief  difference  between  carpus  of  cat  and  man? 

21.  Draw  the  lateral  aspect  of  the  third  metacarpal  and  label  all 
features. 

22.  How  do  you  distinguish  the  distal  from  the  proximal  end  of 
the  metacarpals? 

23.  Describe  the  variation  in  the  number  of  metacarpals  in  mammals. 

24.  Describe  the  usual  arrangement  of  the  phalanges  in  mammals 
having  five  digits. 

25.  How  do  you  distinguish  a  phalanx  from  a  metacarpal? 

26.  Give  the  number  of  functional  digits  in  forelimb  of  dog,  pig, 
cow,  sheep,  horse,  and  rabbit. 

27.  Name  some  mammals  with  atrophied  digits. 

28.  What  is  the  significance  of  these? 

29.  In  the  evolution  of  the  perissodactyls  (odd-toed  ungulates)  de- 
scribe the  order  in  which  the  digits  are  lost. 

30.  In  t;he  Bovidse  and  Cervidae  which  two  digits  are  functional? 


64  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

THE  PELVIC  LIMB. 

The  pelvic  or  hind-limb  of  the  cat  is  composed  of  the 
innominate  bone,  femur,  patella,  tibia,  fibula,  seven  tarsals, 
five  metatarsals,  and  twelve  phalanges. 

The  innominate  bone  is  composed  of  four  parts,  the 
ilium,  ischium,  pubis  (Figs.  21  and  38),  and  the  small 


FIG.  38.  VENTRO  LATERAL  ASPECT 
OF  LEFT  INNOMINATE  BONE  OF  A 
KITTEN. 

ct,  Cot3rloid  bone ;  ac,  acetabulum ; 
il,  ileo-pectineal  eminence ;  as, 
anterior  inferior  spine. —  (Modi- 
fied after  Jayne.} 


FIG.  39.  VENTRAL  ASPECT  OF  THE 
INNOMINATE  BONES. 

ac,  Acetabulum ;  ai,  posterior  infe- 
rior spine ;  ar,  auricular  surface ; 
cr,  crest;  et,  cotyloid  notch;  ip, 
ileopectineal  eminence;  is,  body 
of  ischium;  ob,  obturator  fora- 
men :  pb,  body  of  pubis ;  s,  spine ; 
sm,  symphysis  pubis;  sp,  spine 
of  pubis;  sr,  surface  of  ilium 
for  attachment  of  spinal  mus- 
cles; tb,  tuberosity  of  the  is- 
chium. 


cotyloid  bone.  The  ilium  is  the  dorsal  portion,  extending 
down  to  and  occupying  about  one-third  of  the  acetabulum. 
The  ischium  includes  the  caudal  portion  of  the  bone,  extend- 
ing ventral  and  forming  two-thirds  of  the  boundary  of  the 


THE   SKELETON.  65 

obturator  foramen.  The  pubis  is  the  ventral  portion,  pos- 
sessing two  ratni,  one  projecting  laterad  to  unite  with  the 
ilium,  cotyloid,  and  ischium,  and  the  other  projecting 
caudad  along  the  mid-ventral  line,  joining  its  fellow  and 
the  ischium.  In  young  kittens  the  junction  of  these  parts 
is  plainly  visible,  but  in  adult  specimens  it  is  wholly  oblit- 
erated. In  old  specimens  the  ischium  and  pubis  become 
more  or  less  anchylosed  with  their  fellows  in  the  mid- 
ventral  line.  The  cranial  and  dorsal  border  of  the  ilium  is 
the  crest  (Fig.  39).  The  rough  crescentic  area  on  the 
medial  aspect  is  the  auricular  surface  for  articulation  with 
the  sacrum.  The  cranial  rounded  angle  of  the  crest  is  the 
anterior  superior  spine.  The  anterior  inferior  spine  is  the 
small  prominence  craniad  from  the  ventral  termination  of 
the  auricular  surface. 

The  ischium  presents  a  spine  on  its  dorsal  border  near 
the  acetabulum.  Between  this  spine  and  the  posterior  in- 
ferior spine  of  the  ilium,  is  a  shallow  concavity  termed  the 
greater  sciatic  notch  in  distinction  to  the  lesser  sciatic  notch 

<^ 

between  the  spine  of  the  ischium  and  the  tuberosity.  The 
acetabulum  or  cotyloid  cavity  forms  the  cup  for  the  articu- 
lation of  the  femur.  The  interruption  in  its  ventral  border 
is  the  cotyloid  notch,  at  whose  base  there  is  a  depression  for 
the  attachment  of  the  ligamentum  teres  holding  the  femur 
in  place.  The  junction  of  the  pubis  with  its  fellow  is  known 
as  the  symphysis.  The  cranial  portion  of  the  bone  lying 
on  either  side  of  this  is  called  the  body,  the  caudal  part 
taking  the  name  of  ramus.  The  latter  forms  part  of  the 
boundary  of  the  obturator  foramen  and  meets  the  ramus  of 
the  ischium.  This  foramen  gives  passage  to  the  obturator 
nerve  and  vessels. 

In  the  Sirenia,  which  have  no  pelvic  limbs,  the  innomi- 
nate bones  are  rudimentary.  In  the  Cetacea  these  bones 
are  also  rudimentary,  which  fact  indicates  that  the  ances- 
tors of  these  forms  possessed  functional  hind-limbs. 


66 


ELEMENTS    OF   MAMMALIAN    ANATOMY. 


The  femur,   or  thigh-bone,   may  be   recognized   by   its 
spherical  head  with  a  pit  for  the  attachment  of  the  liga- 


hi 


Lend. I 

FIG.  40.  CAUDAL  ASPECT  OF 
FEMUR. 

ex.  tub,  External  tuberosity ;  int. 
tub,  internal  tuberosity ;  ex. 
end,  external  condyle ;  int. 
end,  internal  condyle ;  i.  end. 
t,  intercondylar  notch  or 
fossa ;  intch.  r,  intertro- 
chanteric  ridge ;  g.  trch, 
greater  trochanter ;  hd,  head  ; 
I'm.  as,  linea  aspera;  /.  trch, 
lesser  trochanter;  nk,  neck; 
pit,  pit  for  the  ligamentum 
teres;  tr.  fos,  trochanteric 
fossa  or  digital  fossa. 


-i  to 


FIG.  41.  ANTERIOR  OR 
CRANIAL  ASPECT  OF 
RIGHT  TIBIA. 

at,  Articulatory  sur- 
face for  the  astrag- 
alus;  cr,  crest;  et, 
external  tuberosity ; 
fc,  facet  for  articu- 
lation with  the  fib- 
ula ;  im,  internal 
malleolus ;  it,  inter- 
nal tuberosity ;  Ig, 
ligament  of  the 
patella  cut  off;  tb, 
tubercle. 


mentum  teres  which  aids  in  holding  the  head  in  the  ace- 
tabulum. 


THE    SKELETON.  67 

The  greater  trochanter  projects  from  the  proximal  end  of 
the  bone  to  a  level  with  the  head.  On  this  process  are 
inserted  the  pyriformis,  gluteus  medius,  and  gluteus  mini- 
mus muscles,  all  of  which  originate  on  the  innominate  bone. 
The.  lesser  trochanter  is  the  small  projection  on  the  caudal 
aspect  of  the  proximal  portion  of  the  bone  (Fig.  40).  The 
intcrkro  chant  eric  ridge  or  posterior  intertrochanteric  line 
extends  between  the  two  trochanters,  and  lying  between 
this  line  and  the  neck  is  the  digital  fossa.  The  external  and 
internal  condyles  are  the  articulatory  processes  on  the  distal 
end  of  the  bone.  The  blunt  projections  at  their  roots  are 
the  external  and  internal  tuberosities.  The  inter  condyloid 
notch  forms  the  depression  on  the  caudal  aspect  between 
the  condyles.  On  the  cranial  aspect  is  the  trochlear  sur- 
face for  articulation  with  the  patella.  Two  small  sesamoid 
bones,  the  fabellae,  are  present  on  the  caudal  aspect  of  the 
condyles,  but  they  are  usually  removed  in  preparing  the 
skeleton.  The  linea  aspera  is  the  slightly  roughened  line 
beginning  on  the  caudal  side,  distal  to  the  middle  and  ex- 
tending proximally  a  short  distance,  where  it  bifurcates. 

The  form  of  the  femur  varies  but  little  among  mammals 
having  functional  posterior  limbs.  No  living  Sirenia  have 
any  trace  of  a  femur,  but  a  vestigial  femur  is  present  in 
Halithcriuni,  a  fossil  form.  The  hind-limbs  are  wanting 
among  the  Cetacea,  but  in  a  few  forms  nodules  of  bone  or 
cartilage  may  represent  the  femur.  In  most  Perissodactyla 
and  Rodentia,  and  in  some  Insectivora  and  a  few  fossil 
Carnivora,  a  third  trochanter  is  present. 

The  patella,  or  knee-cap  (Fig.  21),  is  a  sesamoid  bone 
developed  in  the  tendon  of  the  quadriceps  extensor  muscle 
(Fig.  52).  It  is  somewhat  the  shape  of  an  almond  and 
about  half  its  size.  It  articulates  with  the  trochlea  of  the 
femur. 

The  tibia  is  the  larger  bone  of  the  crus.     It  presents  two 


68 


ELEMENTS    OF   MAMMALIAN    ANATOMY. 


enlarged  extremities  and  a  shaft  whose  cross-section  is  tri- 
angular. It  articulates  with  the  femur  and  fibula  proximally 
and  the  fibula  and  astragalus  distally 
(Fig.  21 ).  This  is  the  longest  bone  in 
the  cat's  skeleton.  Between  the  concave 
condyles  on  the  proximal  end  is  a  notch 
giving  attachment  to  the  crucial  ligament 
of  the  knee-joint  (Figs.  41,  46). 

The  prominences  of  the  lateral  and 
medial  aspects  of  the  proximal  extremity 
are  the  external  and  internal  tuberosities 
respectively.  Beneath  the  former  is  the 
facet  for  articulation  with  the  fibula  (Fig. 
41).  The  tubercle,  a  prominence  on  the 
cranial  side  of  this  extremity,  is  for  the 
insertion  of  the  ligamentum  patellae,  which 
is  really  the  termination  of  the  tendon  of 
the  quadriceps  extensor  muscle  (Fig.  52). 
On  the  caudal  aspect  between  the  con- 
dyles is  the  popliteal  notch.  The  sharp 
cranial  border  of  the  bone  forms  the 
crest.  On  the  distal  extremity  is  a  proc- 
ess, the  internal  malleolus,  bearing  two 
grooves,  the  more  caudal  of  which  shel- 
ters the  tendon  of  the  flexor  longus  digi- 
torum  muscle  while  the  other  is  for  the 
tibialis  posticus  (Fig.  52).  A  facet  is 
present  on  the  lateral  aspect  of  this  ex- 
tremity for  articulation  with  the  fibula. 

The  fibula  in  proportion  to  its  length 
is   the    slenderest   bone   in   the   skeleton. 
It  is  the  outer  or  lateral  bone  of  the  crus,   and   articu- 
lates proximally  with  the  tibia  and  distally  with  the  tibia 
and    astragalus    (Fig.    21).      The   proximal    extremity   is 


FIG.  42.  INNER  OR 
MEDIAL  ASPECT 
OF  RIGHT  FIB- 
ULA. 

a,  Facet  for  tibia ; 
ar,  facet  for  as- 
tragalus ;  ex,  ex- 
ternal malleolus ; 
h, head;  s,  shaft ; 
t,  articular  sur- 
face for  tibia ; 
gr,  groove  for 
peroneus  longus 
muscle. 


THE   SKELETON.  69 

the  head,  upon  which  is  a  circular  facet  for  articulation 
with  the  tibia.  The  sharp  edge  along  the  cranial  aspect 
of  the  shaft  furnishes  attachment  to  the  interosseous  mem- 
brane uniting  the  two  bones  of  the  crus.  The  medial 
aspect  of  the  distal  extremity  shows  a  prominent  facet  for 
articulation  with  the  astragalus.  Immediately  proximal  to 
this  is  the  articular  surface  for  the  tibia.  From  the  lateral 
aspect  projects  the  external  malleolus,  on  the  caudal  side 
of  which  is  a  groove  for  the  peroneus  brevis  muscle,  and 
on  the  cranial  side  is  a  slight  depression  for  the  peroneus 
longus  (Fig.  52). 

In  many  of  the  Mammalia  the  two  bones  of  the  crus  are 
more  or  less  united.  In  most  of  the  Chiroptera  and  Ungu- 
lata  the  fibula  is  rudimentary.  The  middle  portion  of  the 
fibula  is  absent  in  the  horse  and  its  distal  portion  is  fused 
with  the  tibia  (Fig.  35).  The  ancestor  of  the  Equidse  in 
Eocene  times  had  a  well-developed  fibula,  but  in  the  evolu- 
tion of  the  horse  this  bone  has  gradually  diminished  in  size, 
as  shown  in  the  figure. 

The  tarsus  is  composed  of  seven  bones  in  two  rows. 
The  proximal  row  contains  the  os  calcis,  astragalus,  and 
navicular  or  scaphoid ;  the  distal  row  the  cuboid,  and  three 
cuneiform  bones.  The  ay  calcis,  or  calcaneum,  \?,  the  largest 
bone  of  the  tarsus,  being  twice  as  long  as  broad  (Fig.  43). 
Its  caudal  end  presents  a  groove  for  the  tendon  of  the  plan- 
taris  muscle.  The  peroneal  tubercle  is  on  the  outer  side  of 
the  distal  extremity.  The  sustentaculum,  a  shelf -like  process 
projecting  from  near  the  middle  of  the  inner  side,  supports 
a  facet  for  the  tendon  of  the  flexor  longus  digitorum  muscle 

(Fig-  53). 

The  astragalus  lies  on  the  inner  or  medial  side  of  the 
calcaneum  and  articulates  with  the  tibia,  fibula,  calcaneum, 
and  scaphoid.  The  bone  is  composed  of  a  body,  neck,  and 
head.  The  body  is  proximal  and  bears  a  trochlear  surface 


ELEMENTS    OF   MAMMALIAN    ANATOMY. 


for  articulation  with  the  tibia.  The  head  bears  a  convex 
surface  for  articulation  with  the 
navicular.  The  neck  is  the  con- 
stricted portion  between  the  body 
and  the  head. 

The  scaphoid  lies  on  the  medial 
side  of  the  foot  and  articulates  with 
the  remaining  six  bones  of  the  tar- 
sus. It  may  be  recognized  by  its 
deep  concave  surface  for  articulation 
with  the  astragalus,  and  also  by  the 
tuberosity,  a  process  on  its  medial 
plantar  angle  ( Fig.  43 ) . 

The  internal  cuneiform  is  next  to 
the  smallest  bone  of  the  tarsus.  It 
articulates  with  the  navicular,  mid- 
dle cuneiform,  and  first  and  second 
metatarsals.  The  middle  cuneiform 
is  a  wedge-shaped  bone  and  the 
smallest  element  of  the  tarsus.  It 
articulates  with  the  other  two  cunei- 
forms, the  scaphoid  and  second  met- 
atarsal.  The  external  cuneiform 
may  be  recognized  by  a  strong  hook- 
like  process  on  its  plantar  surface. 
It  articulates  with  the  scaphoid, 
middle  cuneiform,  cuboid,  and  sec- 
ond and  third  metatarsals. 

The  cuboid  is  the  lateral  bone  of 
the  distal  row.  It  may  be  recognized 
by  the  deep  groove  on  its  plantar 
surface  which  shelters  the  tendon  of 
the  peroneus  longus  muscle. 
The  typical  arrangement  of  the  tar  sal  elements  in  ver- 


FIG.  43.  DORSAL  ASPECT 
OF  LEFT  HIND-FOOT. 

ag,  Astragalus ;  ar,  artic- 
ular surface  of  the 
tibia;  cb,  cuboid;  ec, 
external  cuneiform ;  gr, 
groove  for  the  tendon 
of  the  plantaris ;  h, 
head  of  the  fourth 
metatarsal;  ic,  internal 
cuneiform;  me,  middle 
cuneiform;  mi,  hallux 
or  first  metatarsal ;  m2, 
w3,  m*,  and  WB,  second, 
third,  fourth,  and  fifth 
metatarsals;  nv,  navi- 
cular or  scaphoid ;  oc, 
os  calcis,  or  calca- 
neum  ;  3,  proximal  row 
of  phalanges ;  2,  mid- 
dle row  of  phalanges ; 
i,  distal  row  of  phalan- 
ges. 


THE   SKELETON.  71 

tebrates  is  similar  to  that  of  the  carpus.  Three  bones,  a 
tibiale,  intermedium,  and  fibula-re,  compose  the  proximal 
row,  while  five  tarsalia  form  the  distal  row.  The  centrale 
occupies  the  center  of  the  tarsal  region.  In  the  adult  mam- 
mal, fusion  of  some  of  these  elements  occurs,  so  that  not 
more  than  seven  distinct  bones  are  present  in  any  form. 
The  astragalus  contains  the  tibiale  and  intermedium,  while 
the  fourth  and  fifth  tarsalia  form  the  cuboid. 

The  metatarsus  consists  of  five  bones,  the  first  of  which 
is  rudimentary,  while  the  other  four  are  longer  than  the 
metacarpus,  which  they  resemble  ( Fig.  43 ) .  The  first  meta- 
tarsal  is  smaller  than  any  bone  of  the  tarsus.  It  articulates 
with  the  internal  cuneiform  and  is  also  in  contact  with  the 
second  metatarsal.  The  four  long  metatarsals  have  a  slight 
dorsal  convexity,  each  one  consisting  of  a  base  or  enlarged 
proximal  part,  a  shaft  or  middle  portion,  and  a  head  or 
distal  rounded  articular  process.  On  the  plantar  surface  of 
the  head  of  each  metatarsal  is  a  median  spine,  on  each  side 
of  which  is  a  concavity  for  a  sesamoid  bone.  These  sesa- 
moid  bones  are  frequently  lost  in  cleaning  the  skeleton. 

The  number  of  functional  metatarsals  in  mammals  varies 
from  one  to  five.  Usually  the  number  of  metacarpals  and 
metatarsals  is  the  same,  but  in  the  tapir  there  are  four  meta- 
carpals and  but  three  metatarsals.  All  Monotremata,  Car- 
nivora,  and  Primates  have  five  metatarsals,  but  in  the  cats, 
dogs,  and  hyenas  the  first  metatarsal  is  vestigial.  In  early 
geological  times  all  mammals  possessed  five  metatarsals,  the 
number  of  which  in  many  cases  has  gradually  diminished 
owing  to  environment,  as  is  shown  in  the  phylogeny  of  the 
horse  (Fig.  35). 

The  Equidae  possess  but  one  functional  metatarsal  and 
two  rudimentary  ones,  although  Orohippus,  the  ancestor  of 
the  horse,  had  three  functional  metatarsals. 

The  phalanges  of  the  cat's  foot  are  twelve  in  number. 


72  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

Each  metatarsal  except  the  first  supports  three  phalanges. 
The  proximal  phalanges  are  the  stoutest,  and  the  distal  the 
smallest.  Each  distal  phalanx  bears  a  claw. 

In  all  five-toed  animals,  such  as  Primates,  there  are  four- 
teen phalanges,  each  digit  being  composed  of  three,  except 
the  hallux,  which  has  two. 

PRACTICAL   QUESTIONS    AND    SUGGESTIONS. 

1.  Describe  the  articulations  of  the  innominate  bone. 

2.  How  do  you  distinguish  the  cranial  from  the  caudal  aspect  of 
the  os  innominatum? 

3.  Which  processes  derive  their  names  from  their  location? 
^•4.  Draw  the  lateral  aspect  of  the  os  innominatum  and  label  all  fea- 
tures. 

5.  Name  the  four  parts  of  the  bone  in  order  of  size. 

6.  What  two  orders  of  mammals  have  no  pelvic  limbs? 

7.  Describe  what  is  seen  in  viewing  the  femur  from  the  cranial 
aspect. 

8.  Name  the  processes  of  the  femur. 

9.  Draw  the  distal  aspect  of  the  femur. 

10.  How  do  you  distinguish  the  right  from  the  left  femur? 

11.  Describe  the  patella. 

12.  Draw  the  caudal  aspect  of  the  tibia  and  label  all  features. 

13.  How  do  you  distinguish  the  right  from  the  left  tibia? 

14.  Describe  the  articulations  of  the  fibula. 

15.  What    features    distinguish   the   proximal    from   the   distal   ex- 
tremities of  the  fibula? 

16.  Write   100  words   describing  the  crus  in  other  mammals  than 
the  cat. 

17.  Draw  the  ventral  aspect  of  the  tarsus  and  label  all  parts. 

18.  Which  of  the  tarsals  support  metatarsals? 

19.  Name  the  tarsals  in  order  of  size. 

20.  Draw  the  lateral  aspect  of  the  third  metatarsal. 

21.  How  do  you  distinguish  a  metatarsal  from  a  metacarpal? 

22.  How  do  you  distinguish  the  proximal  from  the  distal  end  of  a 
metatarsal? 

23.  Describe  the  condition  of  the  metatarsals  in  various  mammals. 

24.  In  most  mammals  how  many  phalanges  to  each  digit? 

25.  What  artiodactyls  have  you  seen  with  only  two  functional  digits 
on  the  posterior  limbs? 


THE  JOINTS. 


The  study  of  the  articulation  of  the  bones  and  the  liga- 
ments holding  them  in  place  is  known  as  syndesmology. 
There  are  three  general  classes  of  articulations :  Synar- 
throses,  or  immovable  joints;  amphiarthroses,  or  joints 
with  slight  motion;  and  diarthroses,  or  joints  freely  mov- 
able. A  synarthrodal  joint  is  exemplified  in  the  sutures  be- 
tween the  bones  of  the  skull.  The  two  surfaces  of  bone  are 
separated  by  fibrous  membrane  only.  An  amphiarthrodal 
articulation  occurs  between  the 
bodies  of  the  vertebrae  and  also  in 
the  union  of  the  sacrum  with  the 
ilium.  In  the  articulation  of  the 
vertebrae  the  contiguous  surfaces 
of  the  bone  are  faced  by  flattened 
discs  of  fibrocartilage  (Fig.  21). 

The  diarthrodal  articulation  is 
exemplified  in  all  joints  allowing 
free  motion.  Such  joints  are 
composed  of  the  following  parts : 
the  ends  of  two  bones  having 
their  contiguous  surfaces  covered 
with  cartilage;  a  synovial  mem- 
brane forming  a  short  tube  whose  ends  are  closed  by  the 
cartilaginous  articulating  surfaces;  and  several  ligaments 
varying  in  number  from  two  or  three  to  a  dozen  (Fig.  44). 
There  are  four  kinds  of  the  diarthrosis :  the  arthrodia,  or 
gliding  joint,  which  occurs  between  the  bones  of  the  carpus : 
the  enarthrosis,,  or  ball-and-socket  joint,  such  as  at  the  hip 
or  shoulder;  the  ginglymus,  or  hinge  joint,  exemplified  at 
the  elbow  and  knee;  and  the  rotatoria,  or  pivot  joint,  formed 
by  the  articulation  of  the  axis  and  atlas. 
8  73 


FIG.    44.      DIAGRAM    OF    A 
DIARTHRODAL  JOINT. 

ar,  Articulatory  cartilage ;  lg, 
ligament ;  sn,  synovial 
membrane ;  sy,  synovial 
fluid  in  synovial  cavity;  t, 
tibia ;  v,  femur. 


74 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


As  the  knee-joint  can  be  readily  dissected  and  the  parts 
well  displayed,  it  is  here  described  somewhat  in  detail.  The 
leg  should  be  detached  at  the  hip- joint  and  the  muscles 
largely  removed,  taking  care  in  the  immediate  neighbor- 
hood of  the  knee  that  the  ligaments  are  not  cut.  There  are 

eight  ligaments  to  this  joint. 
The  anterior  ligament  or 
ligament  of  the  patella 
(Fig.  45),  extending  from 
the  patella  to  the  anterior 
tubercle  on  the  tibia,  is  the 
strongest  ligament  of  the 
knee-joint,  and  is  really  a 
continuation  of  the  tendon 
of  the  quadriceps  extensor 
muscle.  The  capsular  liga- 
ment, which  entirely  sur- 
rounds the  joint  except  in 
the  places  occupied  by  the 
anterior  and  lateral  liga- 
ments, consists  of  two  parts, 
a  cranial  and  a  caudal  por- 


FIG.  45.    LATERAL  ASPECT  OF  DIS- 
SECTED KNEE-JOINT. 


ad,  Adipose  tissue;  ax,  antero-in- 
ternal  ligament  of  the  meniscus ; 
cp,  capsular  ligament  cut  and  re- 
flected mediad;  bi,  tendon  of 
the  popliteus  muscle  pulled 
proximad  to  display  sc;  en, 
caudal  projection  of  condyle  of 
tibia;  ex,  antero-external  liga- 
ment of  the  meniscus;  ex,  ex- 
ternal lateral  ligament;  fb, 
fibula;  fm,  femur;  lg,  ligament 
of  the  quadriceps  extensor 
muscle ;  pt,  patella ;  sc,  external 
or  lateral  meniscus ;  scm,  medial 
or  internal  meniscus ;  tf,  tibio- 
fibular  ligament ;  tb,  tibia. 


tion.  The  former  is  seen 
on  either  side  of  the  anterior 
ligament,  extending  from 
the  femur  to  the  tibia  as  a 
thick  membrane,  and  more 
laterally  being  attached  to 
the  menisci.  The  caudal  part 


extends     from    the    fabellse 
and  the  femur  to  the  tibia  and  menisci. 

The  external  lateral  ligament  proceeds  from  the  external 
tuberosity  of  the  femur  to  the  head  of  the  fibula.  The 
internal  lateral  ligament,  much  shorter  than  the  external 


THE   JOINTS. 


one,  extends  from  the  internal  tuberosity  of  the  femur  to 
the  internal  tuberosity  of  the  tibia.  The  anterior  and  cap- 
sular  ligaments  must  be  cut  in  order 
to  see  the  crucial  ligaments,  which 
are  short,  and  cross  each  other  in 
the  region  of  the  intercondylar  notch. 
The  posterior  crucial  extends  from 
the  caudal  margin  of  the  head  of 
the  tibia  to  the  mediocranial  angle 
of  the  intercondyloid  notch  of  the 
femur.  The  anterior  crucial  extends 
from  the  summit  of  the  tibia  to  the 
caudolateral  angle  of  the  intercondy- 
loid notch.  The  tibiofibular  ligament 
is  very  short,  extending  from  the 
head  of  the  fibula  to  the  outer  tu- 
berosity of  the  tibia.  In  addition  to 
these  ligaments,  there  are  four 
bands  uniting  the  menisci  to  the 
bones.  The  menisci  or  semilunar 
cartilages  are  two  biconcave  car- 
tilaginous plates,  about  one  milli- 
meter thick,  interposed  between  the 
condyles  of  the  femur  and  tibia. 

The  synovial  membrane  is  a  very 
thin  transparent  sheet  lying  within 
the  capsular  sheath  of  the  joint.  It 
secretes  the  white  glairy  synovia  for 
lubricating  the  joint.  The  synovial 
fluid  and  membrane  may  be  demon- 
strated by  cutting  open  a  fresh  joint 
obtained  from  the  butcher-shop  (Fig.  44). 

All  other  freely  movable  joints  are  similar  in  structure  to 
the  knee-joint,  but  have  no  menisci  and  fewer  ligaments. 


FIG.  46.  CAUDAL  ASPECT 
OF  KNEE-JOINT  WITH 
CAPSULAR  LIGAMENT 
CUT. 

ac,  Anterior  crucial  liga- 
ment ;  ar,  articular  sur- 
face of  condyle  of 
tibia ;  en,  condyle  of 
femur ;  cp,  capsular 
ligament  cut  along  the 
line  lg  and  reflected 
proximad ;  ex,  external 
lateral  ligament;  fb, 
fibula ;  fm,  femur ;  in, 
internal  lateral  liga- 
ment; lg,  cut  edge  of 
capsular  ligament;  pc, 
posterior  crucial  liga- 
ment ;  pi,  posterior  ex- 
ternal ligament  of  the 
meniscus ;  sm,  medial 
or  internal  meniscus; 
sme,  lateral  or  exter- 
nal meniscus ;  tf,  tibio- 
fibular ligament ;  tb, 
tibia. 


76  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

The  shoulder- joint  has  only  two  or  three  ligaments,  the 
most  important  of  which  is  the  capsular.  The  elbow- joint 
has  four  ligaments  and  the  hip- joint  only  two.  In  the 
ankle-joint  there  are  eight  ligaments  in  addition  to  the 
capsular. 

These  ligaments  which  bind  the  joints  consist  of  white 
fibrous  connective  tissue  which  under  the  microscope  is  seen 
to  be  composed  of  parallel  and  interlacing  fibers.  They 
are  very  tough  and  have  but  little  elasticity,  so  that  the 
joints  are  seldom  dislocated  (Fig.  n). 

PRACTICAL   QUESTIONS    AND    SUGGESTIONS. 

1.  Give  three  examples  of   each  of  the  three  general  classes  of 
joints. 

2.  Explain  difference  in  anatomy  of  the  three  classes  of  joints. 

3.  Without  aid  of  the  microscope  can  you  detect  any  differences 
between  a  ligament  and  a  tendon? 

4.  By  removing  the  capsular  ligament  describe  the  ligaments  that 
can  be  displayed  on  the  lateral  and  caudal  aspects  of  the  knee-joint. 

5.  After  bringing  to  view  by  dissection  as  many  ligaments  as  pos- 
sible on  inner  aspect  of  knee-joint,  draw  and  label  all  parts. 

6.  Draw  the  menisci. 

7.  By  careful  dissection  note  the  ligaments  present  in  the  hip-joint. 

8.  How  many  ligaments  can  you  find  in  the  shoulder-joint? 

9.  In  what  joints  is  synovia  present? 

10.  Cut  a  very  thin  slice  of  articular  cartilage  about  a  millimeter 
square,  mount  in  dilute  acetic  acid,  and  make  drawing  as  seen  under 
the  microscope. 


THE  MUSCLES. 

The  study  of  the  muscular  system  is  known  as  myology. 
The  muscles  are  of  two  kinds :  voluntary,  which  are  under 
the  control  of  the  will;  and  involuntary,  which  cannot  be 
controlled  by  the  will.  All  muscles  moving  the  bones  are 
voluntary  and  are  supplied  with  branches  of  the  cerebro- 
spinal  nerves.  Examples  of  involuntary  muscles  are  found 
in  the  walls  of  the  alimentary  canal,  the  ureter,  bronchial 
tubes,  and  blood-vessels.  These  are  supplied  with  nerves 

/  Q  ^9 '4^  1^ 

from  the  sympathetic  nervous  system  (Fig$  9*).  The 
structure  of  a  voluntary  muscle  may  be  seen  by  teasing  a 
small  piece  on  a  slide  in  a  drop  of  water,  covering  with  a 
cover-glass,  and  examining  with  the  compound  microscope. 
It  is  composed  of  striated  fibers  from  one  to  fifteen  centi- 
meters in  length,  while  involuntary  muscle  is  composed  of 
cells  more  or  less  spindle-shaped  and  non-striated,  except 
in  the  heart  (Figs.  8  and  10). 

There  are  over  five  hundred  voluntary  muscles  in  the  cat, 
each  of  which  is  usually  attached  at  either  end  to  the  peri- 
osteum of  a  bone.  The  point  of  attachment  on  the  un- 
moved bone  is  known  as  the  origin  of  the  muscle.  The 
insertion  of  a  muscle  is  its  attachment  to  the  bone  which 
it  moves.  In  the  case  of  the  biceps,  its  origin  is  on  the 
scapula  and  its  insertion  on  the  radius.  Usually  a  muscle 
originates  and  terminates  in  a  white  glistening  cord  called 
a  tendon,  composed  for  the  most  part  of  white  fibrous  tis- 
sue (Fig.  n). 

Each  muscle-fiber  is  surrounded  by  a  transparent  elastic 
sheath,  the  sarcolemma.  A  number  of  fibers  bound  together 
by  a  loose  connective  tissue,  and  the  whole  enveloped  by  an 
extension  of  the  same,  is  a  fasciculus.  The  tissue  connect- 

77 


78  ELEMENTS    OF   MAMMALIAN    ANATOMY. 

ing  the  fibers  is  the  endomysium,  while  that  enveloping  the 
fasciculus  is  the  perimysium.  A  number  of  fasciculi  bound 
together  in  a  sheath,  the  epimysium,  constitutes  the  entire 
muscle.  The  epimysium  is  merely  a  deflected  portion  of  the 
sheath  enveloping  the  fasciculus.  It  is  visible  to  the  naked 
eye  as  a  thin  shining  sheath  beneath  the  tougher  fascia 
which  covers  the  muscles  and  binds  them  together. 

According  to  function,  muscles  are  spoken  of  as  flexors, 
extensors,  adductors,  abductors,  rotators,  elevators,  depres- 
sors, and  sphincters.  A  flexor  muscle  is  one  which  by  its 
contraction  bends  a  limb  or  any  portion  of  it.  An  extensor 
muscle  is  the  antagonist  of  a  flexor  and  serves  to  bring  the 
two  long  ^bones  into  line.  An  abductor  muscle  is  the  one 
inserted  on  a  long  bone,  which  it  draws  laterad  from  the 
axis  of  the  limb  or  the  sagittal  plane  of  the  body.  An 
aQductor  muscle  is  the  antagonist  of  an  abductor.  The 
pectoral  muscles  are  adductors  of  the  forelimb.  A  rotator 
muscle  is  one  which  produces  more  or  less  of  a  rotatory 
motion  in  the  bone  upon  which  it  is  inserted.  A  rotator 
muscle  is  exemplified  in  the  obturators,  which  arise  on  the 
innominate  bone  and  are  inserted  in  the  digital  fossa  of  the 
femur.  An  elevator  muscle  is  represented  by  the  temporal, 
extending  from  the  temporal  bone  to  the  mandible,  which 
it  elevates.  A  depressor  muscle  is  the  antagonist  of  an 
elevator.  The  digastric  is  a  depressor  of  the  mandible.  A 
sphincter  muscle  is  one  surrounding  an  orifice  which  it 
closes  by  contraction.  The  orbicularis  oris  in  the  lips  is  an 
example. 

Muscles  are  named  according  to  their  function,  shape, 
or  part  to  which  they  are  attached.  Thus  the  sterno- 
mastoid  muscle  arises  on  the  sternum  and  is  inserted  on  the 
mastoid  process  of  the  skull.  The  latissimus  dorsi  is  so 
named  because  it  is  a  very  broad  muscle  (Fig.  4^)  and 
occupies  the  dorsal  part  of  the  cat's  body.  The  extensor 


THE   MUSCLES.  79 

communis  digitorum  muscle  signifies  by  its  name  that  it  is 
the  common  extensor  of  the  digits. 

DISSECTION  OF  THE  MUSCLES. 

Since  the  other  systems  are  of  more  importance  from  the 
standpoint  of  comparative  anatomy  and  physiology  than  the 
muscular,  only  the  more  important  muscles  will  be  described. 
Great  care  should  be  exercised  in  removing  the  skin  of  the 
cat,  in  order  that  such  superficial  muscles  as  the  platysma 
myoides  on  the  neck  and  side  of  the  face,  and  occipito- 
frontalis,  may  not  be  cut  away.  The  skin  is  attached  to 
the  underlying  muscles  by  the  superficial  fascia,  a  fibrous 
areolar  tissue,  which  contains  the  subcutaneous  fat  more  or 
less  abundant  in  all  specimens.  The  deep  fascia  is  the 
fibrous  and  membranous  layer  of  dense  tissue  lying  close 
against  the  muscles  and  dipping  down  between  them.  The 
stronger  parts  of  this  fascia  are  called  aponeuroses. 

Directions  for  Dissection. — Dissection  does  not  mean 
the  cutting  up,  but  the  intelligent  separation  of  one  organ 
from  another  and  the  removing  of  known  portions  to  study 
the  deeper  structures  more  carefully.  The  muscles  should 
not  be  cut  loose  from  their  origin  or  insertion,  but  merely 
separated  from  each  other  by  cutting  the  deep  fascia  in 
the  longitudinal  direction  of  the  muscle.  If  it  is  neces- 
sary to  remove  a  muscle  for  displaying  those  beneath,  it 
should  be  cut  transversely  in  the  middle  and  the  two  parts 
reflected.  No  portion  of  a  muscle  or  other  tissue  should  be 
removed  without  knowing  what  it  is  and  noticing  carefully 
its  relation  to  the  surrounding  parts.  The  specimen  under 
dissection  should  be  securely  nailed  to  the  tray  so  that  the 
muscles  are  made  tense.  When  the  parts  become  dry,  they 
should  be  thoroughly  wet  with  water.  If  the  formalin  in 
which  the  specimen  has  been  preserved  is  irritating  to  the 
mucous  membrane  of  the  dissector,  a  half  liter  of  5% 
ammonium  hydrate  should  be  poured  over  the  specimen. 


8o  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

The  muscles  of  the  following  table  are  arranged  accord- 
ing to  location,  but  they  need  not  be  dissected  in  the  order 
named.  Some  classes  having  time  for  the  study  of  one- 
half  or  even  one-third  of  the  muscles  here  described  will 
be  able  by  the  use  of  the  table  and  the  illustrations  to  become 
familiar  with  the  functions  and  the  relations  of  any  muscles 
the  instructor  may  wish  to  assign  for  study.  The  student 
should  note  carefully  the  muscles  which  together  effect  a 
certain  motion,  such  as  the  flexion  of  the  forearm  or  the 
extension  of  the  digits. 

FIG.  47.  VENTRAL  ASPECT  OF  THE  CRANIAL  HALF  OF  THE  CAT.  The 
superficial  muscles  have  been  removed  from  the  left  side  and  the 
scapula  reflected  laterad  to  display  the  serratus  and  adjacent  mus- 
cles. 

a,  Triceps ;  b,  triceps ;  cay,  carotid  artery ;  c,  Ci,  and  c2,  scalene  muscles ; 
cph,  cephalohumeral ;  ere,  coracobrachialis ;  dg,  digastric ;  ds,  cut  end 
of  the  digastric;  ext,  external  oblique;  f,  inferior  constrictor;  gh, 
geniohyoid ;  h,  humerus ;  i,  scalene ;  ic,  triangularis  sterni ;  int,  in- 
ternal oblique ;  j,  hyoglossus ;  k,  styloglossus ;  I,  rectus  lateralis ;  Id, 
latissimus  dorsi  reflected  lateral  and  much  of  the  reflected  portion 
cut  off;  lv,  levator  anguli  scapulae;  m,  longus  colli;  man,  mandible; 
mas,  masseter;  mh,  mylohyoid;  md,  median  ventral  line;  n,  fascial 
aponeurosis  of  the  external  oblique ;  pci,  pc2,  pca,  and  pct,  first,  sec- 
ond, third,  and  fourth  parts  of  the  pectoralis  muscle;  pet,  portion 
of  the  pectoral  muscle  of  the  left  side ;  ret,  left  rectus  abdominalis ; 
sh,  sternohyoid ;  shi,  sternohyoid  of  the  left  side  with  its  middle 
portion  removed ;  std,  sternothyroid ;  stm,  sternomastoid ;  st,  por- 
tion of  left  sternomastoid;  sub,  subscapularis;  sps,  suprascapularis ; 
tm,  teres  major;  tr,  triceps;  x,  cleidomastoid ;  i,  2,  3,  7,  8,  and  9, 
ribs ;  5,  trachea. 


THE   MUSCLES. 


81 


FIG.  47- 


82 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


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THE   MUSCLES.  85 


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FIG.  49. 


THE  MUSCLES.  §9 


FIG.  49.     LATERAL  OR  OUTER  ASPECT  OF  MUSCLES  OF  THE  PECTORAL  LIMB. 

a,  Cranial  part  of  the  ento-triceps ;  an,  annular  liagment ;  am,  abductor 
minimi  digiti ;  c,  extensor  carpi  radialis  brevior ;  del,  acromiodeltoid ; 
dl,  biceps;  ecd,  extensor  communis  digitorum;  ecrl,  extensor  carpi 
radialis  longior,  whose  tendon  is  marked  m;  emd,  extensor  minimi 
digiti ;  el,  extensor  indicis ;  exul,  extensor  carpi  ulnaris ;  com,  ex- 
tensor ossis  metacarpi  pollicis ;  ex,  ulnar  head  of  the  flexor  carpi 
ulnaris  ;  fu,  flexor  profundus  digitorum  ;  hu,  humerus  ;  i,  caudal  part 
of  the  ento-triceps ;  o,  olecranon  process  of  the  ulna ;  p,  claw  of  first 
digit;  pect,  portion  of  the  pectoralis ;  r,  region  of  the  head  of  the 
radius ;  sp,  spine  of  the  scapula ;  su,  supinator  longus ;  tr\  ecto- 
triceps  with  its  middle  portion  cut  out. 


90 


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94  ELEMENTS   OF   MAMMALIAN   ANATOMY. 


FIG.  50. 


THE   MUSCLES.  95 


FIG.  50.     MEDIAL  OR  INNER  ASPECT  OF  THE  MUSCLES  OF  THE  FORELIMB. 

a,  Supracondyloid  ridge  of  humerus;  ab,  abductor  pollicis;  b,  humerus; 
c,  humeral  head  of  the  flexor  carpi  ulnaris ;  cp,  ento-triceps ;  d,  in- 
sertion of  a  tendon  of  flexor  sublimis  digitorum ;  e,  ulnar  head  of 
flexor  carpi  ulnaris ;  eci,  extensor  carpi  radialis  longior ;  ecz,  ex- 
tensor carpi  radialis  brevior ;  f,  portion  of  the  flexor  sublimis 
digitorum  arising  from  the  flexor  profundus  digitorum;  fs,  the 
portion  of  the  flexor  sublimis  arising  from  the  palmaris  longus; 
fp,  common  tendon  of  the  flexor  profundus  digitorum ;  fix,  flexor 
profundus  digitorum ;  h,  flexor  profundus  digitorum ;  k,  pronator 
quadratus ;  /,  flexor  carpi  radialis ;  o,  short  part  of  the  ento-triceps ; 
ol,  olecranon  process;  ot,  tendinous  loops;  pect,  pectoralis  cut  off; 
pi,  origin  of  the  palmaris  longus  which  is  reflected  caudad;  pt, 
pronator  teres ;  r,  ento-triceps ;  ro,  coracobrachialis ;  s,  split  in  the 
tendon  of  the  flexor  sublimis  revealed  by  cutting  away  the  tendinous 
loop;  ss,  supraspinatus ;  si,  supinator  longus;  tm,  teres  major;  tb, 
the  head  of  the  humerus ;  x,  a  tendon  of  the  flexor  profundus  digi- 
torum whose  portion  between  the  two  letters  is  cut  out  to  display 
the  insertion  of  d.  ("  Ecto-triceps  "  in  figure  should  be  "  medi- 
triceps.") 


96 


ELEMENTS    OF    MAMMALIAN    ANATOMY. 


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FIG.  51.    VENTRAL  ASPECT  OF  MUSCLES  OF  CAUDAL  PORTION  OF  TRUNK 

AND  THIGH. 

a,  Transversalis  abdominis  becoming  aponeurotic;  adct,  adductor  mag- 
nus ;  c,  pectineus ;  ex.  ob,  external  oblique,  whose  aponeurosis  on  the 
left  side  is  removed;  /,  aponeurosis  of  external  oblique;  grc,  gracilis 
with  its  middle  part  cut  out  on  the  left  side ;  m,  median  ventral 
line ;  ps,  psoas  magnus ;  p,  penis ;  rcf,  rectus  f  emoris ;  ret,  rectus 
abdominis ;  sar,  sartorius  with  its  middle  part  cut  out  on  the  left 
side ;  smb,  semimernbranosus ;  smt,  semitendinosus ;  spmc,  spermatic 
cord;  t,  aponeurosis;  trs,  internal  oblique  with  a  rectangular  piece 
cut  out  to  show  the  rectus  and  transversalis ;  tvg,  tensor  vaginae 
f  emoris;  ts,  testicle;  in,  vastus  internus;  x,  external  abdominal 
ring. 


FIG.  52.  LATERAL  ASPECT  OF  THE  MUSCLES  OF  THE  LEG  WITH  THE 
GLUTEI,  TENSOR  VAGINAE  FEMORIS,  SEMITENDINOSUS,  AND  BICEPS 
FEMORIS  REMOVED. 

a,  Portion  of  semimernbranosus ;  ab,  adductor  magnus ;  b,  peroneus  ter- 
tius;  c,  abductor  ossis  metatarsi;  ct,  cut  surface  of  the  vastus  ex- 
ternus ;  d,  peroneus  brevis ;  eld,  extensor  longus  digitorum ;  gas, 
gastrocnemius ;  I,  tendinous  loop;  Ip,  annular  ligament;  It,  ex- 
ternal lateral  ligament  of  the  knee-joint;  Ig,  tendon  of  the  extensor 
longus  digitorum ;  o,  tendinous  arch  of  the  peroneus  longus ;  oc, 
os  calcis ;  pi,  peroneus  longus ;  ret,  rectus  f  emoris ;  t,  ligamentum 
patellae ;  tr,  greater  trochanter ;  ts,  soleus ;  tg,  tendon  of  gastro- 
cnemius; tpl,  tendon  of  the  plantaris;  ib,  tibialis  antictis;  vex, 
vastus  externus  with  a  piece  cut  out. 


THE   MUSCLES. 


101 


FIG.  51. 


It 


FIG.  52. 


102 


ELEMENTS   OF   MAMMALIAN   ANATOMY, 


The  muscles  in  the  different  orders  of  mammals  have  the 
same  general  arrangement.  Over  four  hundred  muscles 
occurring  in  the  cat  are  found  in  man  and  have  approxi- 
mately the  same  relative  location  and  function,  and  the 
same  nerve-supply.  The  size  and  the 
shape  of  the  muscles  may  vary  somewhat 
in  accordance  with  the  habits  of  the  ani- 
mal. The  pectoralis  in  the  cat  consists 
of  five  parts,  while  in  man  there  are  only 
two  parts.  The  biceps  is  a  simple  muscle 
in  the  cat,  but  in  man  it  has  two  well 
defined  heads.  The  muscles  for  moving 
the  ear,  which  are  well  developed  in  the 
horse,  cow,  and  cat,  are  exceedingly  rudi- 
mentary in  man.  The  Cetacea  and  Sire- 
nia  possess  fewer  muscles  than  the  other 
orders  of  mammals,  as  they  have  no 
hind-limbs.  These  few  remarks  serve  to 
show  that  a  familiarity  with  the  muscles 

-ac  FIG.  53.    CAUDAL  ASPECT  OF  THE  MUSCLES  OF  THE 

CRUS  AND  FOOT  WITH  THE  GASTROCNEMIUS,  SOL- 
EUS,  AND  PLANTARIS  REMOVED. 

ad,  Adductor ;  ac,  tendon  of  Achilles ;  ab,  abductor 
ossis  metatarsi;  eg,  external  head  of  gastrocne- 
mius ;  fb,  flexor  brevis  digitorum  cut  at  x  and 
turned  aside;  fd,  flexor  longus  digitorum,  fl, 
flexor  longus  hallucis;  i,  peroneus  longus;  /, 
peroneus  brevis;  lp,  tendinous  loop  through 
which  pass  the  tendons  of  the  flexor  brevis  digi- 
torum and  the  flexor  longus  digitorum;  n,  cut 
tendons  of  fb ;  o,  plantaris  over  the  tuberosity 
of  the  os  calcis;  p,  tendon  of  the  peroneus 
brevis ;  pi,  tendon  of  the  plantaris,  whose  prox- 
imal portion  is  cut  away ;  r,  tendon  of  the  flexor 
longus  digitorum  pedis  cut  off  as  it  passes 
through  the  slit  in  the  flexor  brevis  digitorum ; 
s,  tendon  of  the  flexor  brevis  digitorum  split 
for  the  transmission  of  the  tendon  of  the  flexor 
longus  digitorum  pedis;  so,  soleus ;  t,  tendon 
of  the  flexor  longus  hallucis ;  x,  plantaris  giving 
origin  to  the  flexor  brevis  digitorum. 


THE   MUSCLES.  103 

of  any  one  mammal  guarantees  a  general  knowledge  of  the 
muscular  system  of  all  mammals. 

PRACTICAL  QUESTIONS  AND  SUGGESTIONS. 

1.  Describe  the  two  kinds  of  muscles. 

2.  Draw  a  diagrammatic  cross-section  of  the  palmaris  longus  muscle 
representing  the  relation  of  the  fibers,  fasciculi,  sarcolemma,  endomy- 
sium,  and  epimysium. 

3.  Describe  an  example  of  each  class  of  muscles  as  to  function. 

4.  Which  muscles  of  the  head  and  neck  region  derive  their  names 
from  their  function? 

5.  Describe  the  chief  muscles  moving  the  mandible. 

6.  Describe  the  muscles  lying  ventral  to  the  trachea. 

7.  Name  three  important  muscles  attaching  the  thoracic  limb  to 
the  trunk. 

8.  Draw  the  caudal  aspect  of  the  triceps  muscle. 

9.  What  muscles  flex  the  forearm  on  the  arm? 

10.  Name  the  chief  extensors  and  flexors  of  the  digits. 

11.  On  what  process  of  the  humerus  do  several  of  the  flexors  of  the 
manus  arise? 

12.  On  what  process  of  the  humerus  do  most  of  the  extensors  of  the 
manus  arise? 

13.  Draw  the  outline  of  the  ventral  aspect  of  the  flexor  profundus 
digitorum  as  it  would   appear   detached   from  limb   and  with   origins 
slightly  separated. 

14.  Draw  cranial  aspect  of  the  radius  and  mark  the  areas  to  which 
the  muscles  are  attached  and  the  names  of  the  same. 

15.  What  muscles  flex  the  manus  on  the  forearm? 

16.  Describe  the  muscles  ^extending  the  manus  on  the  forearm. 

17.  What  muscles  in  the  forearm  region  derive  their  names  from 
their  function  and  location? 

18.  Describe  the  large  adductor  of  the  thoracic  limb. 

19.  Describe  the  muscles  serving  to  move  the  humerus  in  four  direc- 
tions. 

20.  Describe  the  location  and  the  use  of  the  tendinous  loops  in  the 
manus. 

21.  What  muscles  form  the  ventral  and  lateral  walls  of  the  abdomen? 

22.  Describe  from  your  dissection  four  muscles  causing  the  move- 
ment of  the  ribs. 

23.  After  removing  the  biceps  femoris  and  sartorius,  and  dissecting 
the  muscles  on  the  lateral  aspect  of  the  thigh,  draw  the  muscles  visible 
on  the  lateral  aspect,  and  label. 

24.  Name  the  muscles  flexing  the  crus  on  the  thigh. 


104  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

25.  Describe  from  your  dissection  the  muscles  extending  the  crus  on 
the  thigh. 

26.  Describe  the  muscles  forming  the  calf  of  the  leg. 

27.  What  muscles  are  the  opponents  of  the  adductor  magnus? 

28.  Draw  the  plantar  aspect  of  pes  showing  the  superficial  muscles, 
and  label  all  the  features. 

29.  Describe  three  muscles  moving  the  digits. 

30.  Show  by  drawing  the  location  of  the  muscles  flexing  the  pes  on 
the  tibia  and  label  all  the  features. 


ORGANS  OF  DIGESTION. 

A  young  lean  cat  which  has  had  no  food  for  twenty- four 
hours  is  the  best  subject  for  the  demonstration  of  the  di- 
gestive system.  Directions  for  preparing  the  specimen  are 
given  in  the  chapter  on  technique. 

The  digestive  system  (Figs.  55  and  56)  consists  of  the 
alimentary  canal  and  the  accessory  glands  of  digestion. 


. 


FIG.  54.    DIAGRAM  OF  A  GLAND. 

a,  artery ;  v,  -vein ;  c',  part  of  gland  covered  with  capillaries ;   c,  an 
acinus  like  c,  cut  open;  i,  duct. 

The  canal  is  made  up  of  the  mouth,  pharynx,  esophagus, 
stomach,  small  intestine,  and  large  intestine.  Its  entire 
length  is  about  five  times  that  of  the  cat  from  the  tip  of  the 
nose  to  the  root  of  the  tail.  The  accessory  glands  consist 
of  five  pairs  of  salivary  glands,  the  liver,  and  the  pancreas. 

105 


io6 


ELEMENTS   OF   MAMMALIAN   ANATOMY. 


ORGANS    OF   DIGESTION.  107 

A  gland  is  a  tiny  tube  or  collection  of  branching  tubes  which 
remove  certain  materials  from  the  blood  and  manufacture 
them  into  a  fluid  useful  to  the  body. 

THE  MOUTH. 

The  mouth  is  bounded  craniad  by  the  lips,  laterally  by 
the  cheeks,  and  dorsally  by  the  palate,  where  the  mucous 
membrane  lies  in  seven  or  eight  transverse  ridges  or  rugae, 
and  caudally  depends  from  the  palatine  bones  forming  the 
velum  palati.  To  display  the  anatomy  of  the  mouth,  one 
should  remove  the  right  half  of  the  mandible.  From 
either  side  of  the  velum  palati  two  folds  of  membrane  di- 
verge as  they  extend  to  the  floor  of  the  mouth  at  the  root 
of  the  tongue.  The  cranial  fold  is  the  anterior  pillar  and 
the  caudal  one  is  the  posterior  pillar  of  the  fauces  (Fig. 
56).  The  caudal  portion  of  the  mouth  between  these  folds 
is  known  as  the  fauces.  It  opens  into  the  pharynx.  On 
either  side  of  the  tongue  between  the  two  pillars  is  a 
crescentic  depression  holding  a  tonsil.  In  man,  the  tonsils 
sometimes  become  inflamed  and  enlarged,  giving  rise  to  a 
disease  called  tonsilitis.  The  tonsil  is  a  compound  lym- 
phatic gland  whose  function  is  unknown. 

Folds  of  mucous  membrane  called  frena  bind  the  lips  to 
the  gums  which  are  composed  of  dense  fibrous  tissue  in- 
vesting the  alveolar  margins  of  the  jaw-bones.  The  mucous 
lining  of  the  mouth  contains  many  simple  mucous  glands 
invisible  to  the  naked  eye.  Those  of  the  lips  are  called 
labial,  of  the  cheeks,  buccal,  and  of  the  palate,  palatine 
glands. 

The  tongue  lying  in  the  floor  of  the  mouth  is  a  muscular 
mass  composed  of  the  geniohyoglossus,  lingualis  superfici- 
alis  superior  and  inferior,  styloglossus,  and  hyoglossus  mus- 
cles. Caudally  it  is  attached  to  the  hyoid  bone.  Its  invest- 


loS 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


cc 


cd 


ment  of  mucous  membrane  is  formed  into  a  fold  beneath 
it,  called  the  frenum  lingua.     The  dorsal  surface  of  the 

tongue  displays  four  kinds  of 
papillae  (Fig.  56)  :  The  circum- 
vallate,  numbering  from  six  to 
eight  arranged  in  a  V  shape 
near  the  root;  the  flat,  very 
numerous  at  the  root ;  the  con- 
ical, most  numerous  and  thickly 
set  over  the  entire  dorsal  aspect ; 
and  the  fungiform,  which  are 
blunt  and  located  more  thickly 
on  the  sides  and  near  the  tip 
of  the  tongue  (Fig.  56). 

The  Teeth. — During  the 
first  year  the  cat  develops 
twenty-six  teeth,  known  as  the 
deciduous  or  temporary  set,  a? 
they  are  later  replaced  by  a 
permanent  set.  The  three  parts 
of  a  tooth  are  the  crown,  neck, 
and  fang  (Fig.  58).  The 
crown  may  be  divided  into 
several  portions  called  cusps.  A 
tooth  split  longitudinally  pre- 
sents the  following  four  fea- 
tures (Fig.  57)  :  the  enamel,  a 
hard  glistening  substance  cover- 
ing the  entire  crown  of  the 
tooth  down  to  the  neck;  the 
cement,  a  bony  substance  in- 
vesting the  fang;  the  dentine, 
forming  the  interior  hard  por- 
tion of  the  tooth;  and  the  pulp  cavity,  containing  in  tht 


FIG.    56.      DORSAL    ASPECT    OF 
THE  TONGUE  AND  LARYNX. 

at,  Arytenoid  cartilage;  af,  an- 
terior pillar   of   the    fauces; 

cc,  crico-epiglottic  ligament; 

cd,  true  vocal  cords ;  cv,  cir- 
cumvallate   papilla;    ep,   epi- 
glottis;   fl,    flat   papilla;    fg, 
fungiform    papilla ;    fr,    fili- 
form papilla;  gl,  glottis;  hy, 
epihyal  bone  cut  off;  i,  false 
vocal  cord;  as,  lumen  of  the 
esophagus,   which  is  cut  off 
just    as    it    opens    into    the 
pharynx;    pf,    posterior    pil- 
lar of  the  fauces;  in,  tonsil. 


ORGANS    OF   DIGESTION.  109 

recent  state  the  nerve-  and  blood-vessels.  The  enamel  con- 
sists mostly  of  the  phosphate  of  lime.  It  is  the  covering 
which  when  broken  permits  the  tooth  to  decay. 

In  an  adult  cat  there  are  in  each  half  of  the  upper  jaw 
three  incisors,  one  canine,  three  premolars,  and  one  molar 
(Fig.  58).  In  each  half  of  the  lower 
jaw  there  are  three  incisors,  one  ca- 
nine,  two  premolars,  and  one  molar. 
The  permanent  dentition  of  the  cat  is 
therefore  expressed  by  the  formula 
i  %,  c  %,  pm  %,  m  %. 

The  upper  incisor  teeth  are  small  and 

j.    •  i   j  i     .•-,  -,  FIG.     57.       LONGITU- 

undivided  both  as  to  root  and  crown.         DINAL    SECTION    OF 

They  are  scarcely  one-third  as  long  THE  CANINE  TOOTH. 
as  the  canine  and  are  planted  in  the  '^TeminefT^n- 

alveoli  or  sockets  of  the  premaxillary.         amel  >  f>.  f ans >  m> 
rr^,  .    .  ....  pulp-cavity ;  n,  neck. 

I  he  remaining  teeth  of  this  jaw  are  in 

the  maxilla.  The  canine  or  eye  tooth  is  the  longest  and 
likewise  is  undivided  as  to  root  and  crown.  The  next  three 
teeth  are  known  as  the  premolars.  They  vary  much  in  size. 
The  anterior  one  is  the  smallest,  being  about  the  size  of  the 
incisors.  Its  crown  is  usually  simple,  although  occasionally 
there  is  seen  a  small  posterior  cusp,  called  triticone,  in  dis- 
tinction to  the  main  cusp  or  protocone.  The  root  is  usually 
composed  of  only  one  fang.  The  second  premolar  is  much 
larger  than  the  first.  Its  crown  presents  a  large  median 
cusp,  or  protocone;  a  very  small  cusp,  triticone,  on  the 
posterior  side  of  the  protocone  half-way  between  its  base 
and  apex;  and  a  basal  cusp,  the  talon,  on  the  posterior  side 
of  the  base  of  the  tooth.  The  prominent  ridge  encircling 
the  tooth  at  its  base  is  the  cingulum.  The  root  is  composed 
of  two  fangs. 

The  third  premolar  or  carnassial  tooth  is  fully  twice  as 
large  as  the  second  premolar.     Its  protocone  is  the  large 


no  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

( 

central  cusp,  posterior  to  which  is  the  large  triticone.  At 
the  medial  anterior  angle  is  the  deuterocone.  The  small 
projection  at  the  lateral  anterior  angle  is  the  protostyle. 


r  ft  If! 

\i  i/i/ 


FIG.  58.    LATERAL  ASPECT  OF  THE  PERMANENT  DENTITION  OF  THE  CAT. 

ii,  fc,  ia,  First,  second,  and  third  incisors  of  the  upper  jaw;  c,  canine;  pi, 
p2,  and  p3,  first,  second,  and  third  premolars ;  m,  molar ;  i,  2,  3,  the 
incisors  of  the  lower  jaw;  4,  canine;  5  and  6  first  and  second  pre- 
molars ;  7,  molar ;  c,  cingulum ;  d,  deuterocone ;  m,  metaconid ;  m, 
molar ;  pt,  protoconid ;  re,  protocone ;  id,  talonid ;  t,  talon ;  tr, 
triticone. 

The  root  of  the  tooth  usually  consists  of  three  fangs.  The 
posterior  tooth  in  the  maxilla  is  called  the  molar,  since  it  is 
the  only  one  not  preceded  by  a  milk  tooth.  It  is  very  small 
and  its  crown  presents  a  grinding  surface  instead  of  a 
cutting  one.  Its  root  consists  of  two  fangs. 

Each  half  of  the  mandible  holds  three  incisors,  one 
canine,  two  premolars,  and  one  molar.  The  incisors  and 
canine  are  so  similar  to  the  upper  ones  that  they  need  no 
further  description.  The  first  premolar  presents  a  princi- 
pal cusp  or  protoconid,  a  lower  small  cusp  or  metaconid, 
and  a  projection,  on  the  posterior  side  of  the  base,  known 
as  the  talonid.  A  cingulum  or  encircling  ridge  is  also  pres- 
ent at  the  base  of  the  tooth.  The  root  consists  of  two 
fangs. 

The  second  premolar  is  very  similar  to  the  first  except 


ORGANS    OF  DIGESTION.  m 

that  it  is  larger  and  presents  an  anterior  basal  cusp  in  addi- 
tion to  the  others.  The  lower  molar,  sometimes  called  the 
sectorial,  because  it  shears  against  the  upper  sectorial  or 
carnassial  premolar,  presents  two  nearly  equal  cusps,  the 
protoconid  and  the  paraconid.  The  root  consists  of  two 
fangs,  the  anterior  of  which  is  the  larger. 

The  deciduous  or  milk  teeth  begin  to  appear  above  the 
gums  when  the  kitten  is  two  weeks  old.  The  incisors  and 
the  canine  appear  first,  then  the  second  and  third  molars. 
The  first  upper  molars  do  not  appear  till  the  kitten  is  about 
six  weeks  old.  According  to  Jayne,  the  deciduous  dentition 
is  complete  at  the  end  of  the  second  month.  At  the  end  of 
the  fourth  month  the  milk  incisors  are  being  displaced  by 
the  permanent  teeth.  The  formula  for  the  temporary  set 
is  di  %,  dc  %,  dm  %. 

Teeth  are  present  in  nearly  all  adult  mammals.  The 
whalebone  whales,  the  duck-bill,  and  some  of  the  ant-eaters 
have  no  teeth  in  the  adult  state,  but  teeth  are  present  during 
their  embryonic  life.  The  Echidna  shows  no  evidence  of 
teeth  at  any  time.  Most  mammals  have  two  distinct  sets  of 
teeth,  known  as  the  milk  or  deciduous  set,  and  the  perma- 
nent set.  In  the  Marsupialia,  the  milk  dentition  is  in  a 
degenerate  condition.  .  The  milk  teeth  are  present,  but  none 
become  sufficiently  developed  to  appear  above  the  gums,  ex- 
cept the  last  premolar,  and  in  some  cases  the  canine  and  the 
incisors.  The  sloths  have  only  one  set  of  teeth  and  are 
therefore  Monophydont.  Mammals  having  both  a  milk  and 
a  permanent  set  are  termed  Diphydont. 

In  the  majority  of  mammals  the  teeth  are  divided  accord- 
ing to  form  and  function  into  four  groups:  incisors, 
canines,  premolars,  and  molars.  Such  a  dentition  is  known 
as  Heterodont,  in  distinction  to  the  Homodont  dentition, 
in  which  all  the  teeth  have  the  same  form,  as  is  the  case  in 
the  dolphins.  In  mammals  with  a  heterodont  dentition  the 


12 


ELEMENTS    OF   MAMMALIAN   ANATOMY.. 


number  of  teeth  in  the  different  genera  varies  considerably, 
as  seen  by  the  following  formula: 


Pig  

c  4 

P 

-S  
JJog  

r   * 

Pi  '. 

Cat  

<• 

Pj. 

p   i 

Sheep  

C      T 

Horse  

cj 

P  ' 

Opossum  

c*l 

P3 

Man.. 

i 

T 
.  c  i 

D    ^ 

m.f  =  32 


The  elephant  presents  a  very  specialized  dentition.  It 
has  no  canines  nor  any  lower  incisors.  The  single  pair  of 
upper  incisors  is  developed  into  long  tusks,  much  prized  for 
ivory.  They  continue  to  grow  throughout  the  entire  life 
of  the  animal.  Six  molars  are  present  on  each  side,  only 
one  or  two  of  which  are  functional  at  once.  The  posterior 
ones  move  forward  to  take  the  place  of  the  anterior  as  these 
become  worn  out.  The  tusks  of  the  walrus  are  its  canines 
greatly  developed.  None  of  the  typical  modern  Ruminants 
have  upper  incisors  in  the  adult  state,  though  they  are 
present  in  the  embryo.  Palaeontology  has  demonstrated 
that  the  ancestors  of  the  Ruminants  had  well-developed 
upper  incisors  in  the  later  Eocene  times.  The  occurrence 
of  the  rudimentary  upper  incisors  in  the  embryo  furnishes 
evidence  of  a  full  dentition  in  the  ancestors  of  the  rumi- 
nants, since  the  individual  embryological  history  is  some- 
what of  a  recapitulation  of  the  ancestral  history  of  the  race. 

THE  PHARYNX. 

The  pharynx  is  that  portion  of  the  alimentary  canal  be- 
tween the  mouth  and  the  esophagus.  The  structure  is  well 
shown  by  making  a  sagittal  section  through  the  head  and 
neck.  This  is  best  done  with  a  saw,  after  the  specimen  is 
frozen  by  placing  it  out-of-doors  during  one  or  two  days 
of  cold  winter  weather. 


ORGANS    OF   DIGESTION.  113 

There  are  seven  openings  into  the  pharynx:  the  two 
posterior  nares  (Fig.  18),  opening  anteriorly  from  the- 
reof; a  Eustachian  tube  on  each  side;  the  esophagus;  and 
the  larynx,  leading  into  the  trachea.  The  mucous  mem- 
brane lining  the  pharynx  contains  many  simple  microscopic 
mucous  glands. 

VISCERA. 

The  body  cavity  known  as  the  ccelom  must  be  opened 
before  the  rest  of  the  alimentary  canal  can  be  displayed. 
The  entire  ventral  wall  of  the  thoracic  and  abdominal  cavi- 


FIG.  59.    VISCERA  OF  THE  HUMAN  BODY.— (Deaver.} 
co,  Colon;  li,  liver;  lu,  lung;  si,  small  intestine;  st,  stomach. 


IH  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

ties  should  be  cut  away  with  the  bone  forceps  and  scalpel. 
The  body  cavity  is  divided  into  two  parts  by  the  diaphragm 
(Fig.  55).  The  cranial  portion,  the  thoracic  cavity,  con- 
tains the  esophagus,  heart,  blood-vessels,  thoracic  duct, 
trachea,  and  lungs.  In  the  young  cat  there  is  present  also 
the  thymus  gland,  stretching  craniad  several  centimeters 
from  the  base  of  the  heart.  The  transparent  membrane 
lining  this  cavity  and  investing  the  lungs  is  the  pleura. 

The  caudal  part  of  the  coelom  is  the  abdominal  cavity 
containing  the  abdominal  viscera,  which  are  here  briefly 
described.  The  liver,  a  large  brownish-red  organ,  is  ad- 
jacent to  the  diaphragm  on  the  right  side,  while  the  stomach 
(Fig.  55)  lies  close  to  the  diaphragm  on  the  left.  The 
spleen  is  the  dark  red,  flat,  elongated  organ  caudad  of  the 
stomach  on  the  left  side.  The  sheet  of  thin  transparent 
tissue  more  or  less  laden  with  fat,  depending  from  the 
stomach  and  covering  the  intestines  like  an  apron,  is  the 
greater  omentum.  It  is  a  portion  of  the  peritoneum  which 
lines  the  abdominal  cavity  and  invests  most  of  the  organs 
therein.  The  pancreas  is  a  pinkish  elongate  body,  bent  at  a 
right  angle  near  its  middle,  so  that  one  portion  lies  in  the 
bend  of  the  duodenum  and  the  other  dorsal  to  the  stomach. 
The  kidneys  may  be  recognized  by  their  well-known  shape 
and  dorsal  location  in  the  cranial  lumbar  region.  The 
ovaries  are  small  pinkish  bodies  lying  near  the  kidneys, 
adjacent  to  the  dorsal  abdominal  wall.  The  uterus  is  easily 
known  by  its  two  horns  extending  caudad  from  the  ovaries 
to  their  junction  at  the  body  of  the  uterus.  The  bladder, 
if  full  of  urine,  is  at  once  recognized ;  and  if  empty,  appears 
as  a  small  hard  pear-shaped  mass  ventrad  to  the  rectum 

(Fig.  55). 

ESOPHAGUS. 

The  esophagus  or  gullet  is  that  portion  of  the  alimentary 
canal  leading  from  the  pharynx  to  the  stomach.  In  the 


ORGANS    OF   DIGESTION.  115 

thoracic  cavity  it  lies  dorsal  to  the  heart  (Fig.  55)  by  the 
side  of  the  aorta.  Immediately  caudad  of  the  diaphragm 
it  opens  into  the  cardiac  end  of  the  stomach  (Fig.  60). 

STOMACH. 

The  stomach  is  that  dilated  portion  of  the  canal  lying 
immediately  caudad  of  the  diaphragm  on  the  left  side.  The 
esophageal  end  of  the  stomach  is  known  as  the  cardiac  por- 
tion, and  the  intestinal  end  is  the  pyloric  portion  (Fig.  60). 
Here  a  circular  fold  of  mucous  membrane  embraced  by  a 
sphincter  muscle  serves  as  a  valve  to  open  and  close  the 
pylorus  or  gateway  to  the  intestine.  The  dorsal  surface  of 
the  stomach  is  its  lesser  curvature  and  the  ventral  convex 
surface  is  its  greater  curvature.  The  structure  of  the  walls 
of  the  stomach  is  described  below. 

INTESTINE. 

The  intestine  is  that  much  contorted  portion  of  the  canal 
leading  from  the  stomach  to  the  external  aperture  or  anus. 
The  first  portion,  the  small  intestine  (Fig.  60),  is  about 
three  feet  long  in  a  large  cat,  and  is  less  in  diameter  and 
much  more  convoluted  than  the  second  portion,  or  large 
intestine. 

The  small  intestine  consists  of  three  parts:  the  duode- 
num, the  jejunum,  and  the  ileum.  The  duodenum  is  the 
first  twelve  or  fifteen  centimeters.  A  duct  from  the  liver 
and  the  gall-bladder  and  two  ducts  from  the  pancreas, 
empty  into  it.  The  former  is  the  common  bile  duct  and 
the  latter  are  the  pancreatic  ducts.  The  jejunum  is  the 
portion  of  the  small  intestine  next  to  the  duodenum.  It 
is  about  twenty-five  centimeters  long.  No  special  mark 
indicates  its  limits.  It  is  so  called  because  that  portion 
of  the  canal  in  man  is  frequently  empty  after  death.  The 


n6 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


ileum  constitutes  more  than  two-thirds  of  the  small  intes- 
tine, is  much  convoluted,  and  extends  from  the  jejunum 
to  the  large  intestine  on  the  right  side  of  the  abdominal 


FIG.  60.    VENTRAL  ASPECT  OF  THE  ALIMENTARY  CANAL  WITH  THE  ILEUM 
PULLED  TO  ONE  SIDE. 

ac,  Small  intestine  opening  into  the  large  intestine ;  a,  anus ;  ao,  ascend- 
ing colon;  bd,  hepatic  duct;  ce,  caecum;  cd,  cystic  duct;  cs,  bile-cyst 
or  gall-bladder ;  cr,  cardiac  portion  of  the  stomach ;  di,  diaphragm ; 
du,  duodenum ;  do,  caudal  part  of  the  descending  colon ;  dc,  com- 
mon bile  duct ;  gc,  greater  curvature  of  the  stomach ;  il,  ileum ; 
je,  jejunum;  Ic,  lesser  curvature  of  the  stomach;  cc,  esophagus; 
pn,  pancreas ;  py,  pyloric  portion ;  pa,  mesenteric  gland ;  pd,  pan- 
creatic duct;  r,  rectum;  sp,  spleen;  tc,  transverse  colon. 


ORGANS    OF   DIGESTION. 


117 


cavity,  near  the  iliac  bone.     The  intestine  is  supported  by 
the  folds  of  the  peritoneum  known  as  the  mesenteries. 

The  large  intestine  consists  of  the  cacum,  colon,  and 
rectum.     The  ccccum  is  the  blind  conical  projection  at  the 


FIG.  61.     TRANSVERSE  SECTION  OF 
THE   CAT. 

t,  Sections  of  the  intestine;  d, 
duodenum;  a,  aorta;  pan,  pan- 
creas ;  pa,  pancreas  Aselli ;  spl, 
spleen ;  sp,  spinous  process  of 
the  lumbar  vertebra ;  tr,  trans- 
verse process ;  v,  post-cava  or 
inferior  vena  cava ;  om,  greater 
omentum ;  the  broken  line,  is  the 
peritoneum. 


FIG.  62.  CROSS-SECTION  OF  THE 
CARDIAC  END  OF  THE  STOMACH. 
X3- 

cav,  Cavity  of  the  stomach;  ex, 
external  muscular  coat ;  in,  in- 
ternal muscular  coat ;  m,  mu- 
cous coat;  mm,  muscularis 
mucosae;  s,  submucous  or  are- 
olar  coat ;  se,  serous  or  peri- 
toneal coat. 


beginning  of  the  large  intestine.  It  is  only  one  or  two 
centimeters  long.  There  is  no  vermiform  appendix  in  the 
cat.  The  ileum  opens  into  the  large  intestine  at  the  junc- 
tion of  the  caecum  and  colon.  An  annular  fold  of  mucous 
membrane,  strengthened  by  a  sphincter  muscle,  forms  the 
ileocaecal  valve,  which  retains  the  food  in  the  small  intestine 
until  the  nutriment  is  absorbed  (Fig.  60). 

The  colon,  extending  from  the  caecum  to  the  rectum,  is 
composed  of  the  ascending,  transverse,  and  descending 
parts.  The  ascending  colon  lies  on  the  right  side ;  the  trans- 


n8 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


verse  extends  crosswise,  connecting  the  ascending  with  the 
descending,  which  lies  on  the  left  side.  The  descending- 
colon  terminates  in  the  rectum,  which 
is  five  or  six  centimeters  long. 

The  wall  of  the  alimentary  canal 
is  composed  of  three  chief  coats — mu- 
cous, areolar,  and  muscular.  These 
coats  may  be  seen  by  cutting  trans- 
versely, with  a  sharp  scalpel,  a  portion 
of  the  stomach  hardened  in  formalin. 
The  mucous  coat  (Fig.  62)  lines  the 
lumen  and  contains  the  numerous 
glands  which  vary  much  in  the  differ- 
ent portions  of  the  canal.  The  esoph- 
agus contains  the  esophageal  glands, 
whose  secretion  probably  has  no  other 
effect  on  the  food  than  to  facilitate  its 
passage.  The  mucous  coat  of  the 
stomach  contains  the  gastric  glands, 
which  yield  pepsin  and  hydrochloric 
acid,  the  chief  agents  of  the  gastric 
digestive  fluid  (Fig.  63).  The  glands 
in  the  cardiac  end  of  the  stomach  differ 
from  those  in  the  pyloric  end  in  con- 
taining numerous  parietal  or  acid  cells 
which  probably  secrete  the  hydro- 
chloric acid  for  digestion. 

The  mucous  coat  of  the  small  intes- 
tine contains  tube-like  glands,  the 
glands  of  Lieberkiihn,  whose  secretion 
In  the  duodenum  and  jejunum  the  mu- 
cous membrane  is  thrown  into  numerous  transverse  folds, 
valvuli  conniventes,  which  increase  the  surface  for  absorp- 
tion. The  villi  are  minute  finger-like  processes  (Fig.  64), 


FIG.    63.      A    CROSS - 

SECTION  OF  THE  MU- 
COUS COAT  OF  THE 
STOMACH  BETWEEN 
THE  LINES  a  AND  c 
IN  FIG.  60  SHOWS 
A  GASTRIC  GLAND. 
X  250.  Diagram- 
matic. 

a,  Mouth  of  gastric 
gland ;  e,  columnar 
epithelial  cells  on 
the  food  surface  of 
the  stomach ;  /,  lu- 
men of  a  gland;  o, 
oxyntic  or  acid  cell. 

acts  on  the  sugars. 


ORGANS   OF  DIGESTION. 


119 


barely  apparent  to  the  naked  eye,  projecting  into  the  lumen 
for  the  purpose  of  absorbing  the  nutriment  from  the  chyle_ 
They  consist  of  a  covering  of  columnar  epithelial  cells  (Fig. 
65),  within  which  ends  a  chyle  vessel  or  lacteal  surrounded 
by  small  blood-vessels  held  in  place  by  connective  tissue. 
The  fatty  portions  of  the  food  are  carried  by  the  lacteals 
(Fig.  65^)  to  the  left  thoracic  duct,,  and  thence  to  the  jugu- 
lar vein,  while  other  portions  of  the  food  are  taken  up  by 
the  capillaries  of  the  portal  system,  which  begin  in  the  villi 
(Fig.  65).  The  mucous  membrane  of  the  large  intestine 


FIG.  64.  CROSS-SECTION 
OF  THE  SMALL  INTES- 
TINE. X  5. 

ex,  Longitudinal  muscu- 
lar coat ;  m,  circular 
muscular  coat ;  mu, 
mucous  coat ;  Ib,  glands 
of  Lieberkuhn ;  se, 
serous  or  peritoneal 
coat ;  sm,  submucous 
or  areolar  coat. 


FIG.  6$a.    DIAGRAM  OF  A  SMALL  CUBE  CUT 
FROM  THE  WALL  OF  THE  JEJUNUM. 

a,  Mouth  of  intestinal  or  Lieberkuhn's 
glands ;  b,  one  of  the  nine  villi  cut  open 
showing  the  network  of  capillaries  and 
central  white  lacteal  within;  e,  lacteal; 
i,  intestinal  glands;  m,  artery;  v,  vein; 
/  and  t,  muscular  coats. 


likewise  contains  tube-like  glands  similar  to  the  glands  of 
Lieberkuhn,  but  no  villi. 


120 


ELEMENTS   OF   MAMMALIAN   ANATOMY. 


FIG.  6$b.     LACTEALS  AND  PORTAL  SYSTEM  OF  DOG. 

a,  inferior  mesenteric  vein ;  b,  gall  bladder ;  c,  caecum ;  d,  duodenum ; 
e,  esophagus;  i,  parotid  gland;  j,  jejunum;  /,  branches  of  portal 
vein  in  liver;  lu,  branches  of  trachea  and  pulmonary  artery  in  the 
lung;  m,  ilium;  ol,  colon;  p,  pancreas;  s,  spleen;  st,  stomach;  th, 
thoracic  duct  into  which  empty  the  white  tubes,  the  lacteals. 


ORGANS    OF   DIGESTION.  121 

The  sub  mucous  or  areolar  coat  is  adjacent  to  the  mucous 
coat  of  the  intestine,  but  in  the  stomach  the  muscularis 
mucosse  intervenes.  Next  to  the  submucous  coat  is  tHe 
muscular  coat,  composed  of  two  layers,  one  of  circular 
fibers,  the  other  of  longitudinal  fibers.  An  additional  layer 
of  oblique  fibers  is  present  in  the  cardiac  end  of  the  stom- 
ach, which  aid  in  giving  that  organ  the  peculiar  churning  or 
peristaltic  motion  necessary  for  chymification  of  the  food. 
A  fourth  coat  or  serous  covering  surrounds  the  muscular 
coat  of  the  stomach  and  intestines.  It  is  merely  a  reflected 
portion  of  the  peritoneum  which  lines  the  entire  abdominal 
cavity. 

THE  ACCESSORY  GLANDS  OF  DIGESTION. 

The  salivary  glands  are  five  in  number  on  each  side  of 
the  head.  They  secrete  the  saliva,  certain  elements  of 
which  have  the  power  of  changing  starch  into  sugar. 

The  parotid  gland  is  the  largest  of  the  salivary  group 
and  lies  just  ventrad  to  the  base  of  the  external  ear  (Fig. 
66)  beneath  the  skin.  It  is  flat  and  about  two  centimeters 
in  diameter.  Its  secretion  is  poured  into  the  mouth  through 
Stenson's  duct,  which  may  be  seen  extending  from  the 
cranial  margin  of  the  gland  over  the  masseter  muscle,  to 
near  the  angle  of  the  mouth,  where  it  perforates  the  bucci- 
nator muscle,  and  opens  within  the  mouth  on  the  cheek, 
opposite  the  prominent  cusp  of  the  last  premolar.  The 
duct  and  gland  may  be  injected  with  Berlin  blue  by  insert- 
ing the  cannula  into  the  orifice  of  the  duct  (Fig.  66). 

The  submaxillary  gland  is  near  the  angle  of  the  man- 
dible and  ventrad  to  the  parotid.  Wharton's  duct  extends 
from  its  anterior  surface,  between  the  digastric  and  masse- 
ter muscles,  to  its  orifice  on  the  floor  of  the  mouth,  opposite 
the  last  tooth  of  the  mandible. 

The  sublingual  gland  is  quite  small,  elongated,  and  lies 

12 


122 


ELEMENTS   OF   MAMMALIAN   ANATOMY. 


craniad  of  the  submaxillary.  Its  duct  extends  parallel  with 
that  of  the  submaxillary  and  opens  within  the  mouth  upon 
the  same  papilla  beneath  the  tongue.  The  molar  gland  is 

very  small  and  lies  near  the 
angle  of  the  mouth  ventrad 
of  Stenson's  duct.  Its  sev- 
eral ducts,  which  are  not 
easily  demonstrated,  pass 
through  the  cheek  to  open 
within  the  mouth.  The  zy- 
gomatic  or  infraorbital  gland 
lies  on  the  lateral  part  of  the 
orbit  on  the  ventro-lateral 
surface  of  the  eyeball.  It 
may  be  seen  by  cutting  away 
the  zygomatic  arch  and  the 
masseter  muscle.  From  near 
the  ventral  angle  of  the  gland 
a  duct  leads  to  the  roof  of  the  mouth  posterior  to  the  molar 
tooth. 

The  liver  is  the  largest  gland  in  the  body  and  is  situated 
immediately  caudad  of  the  diaphragm  (Fig.  55),  and  in 
contact  with  the  right  lateral  and  cranial  surfaces  of  the 
stomach.  It  is  strongly  convex  on  its  cranial  aspect  while 
its  opposite  surface  presents  a  deep  concavity  occupied  by 
the  stomach.  Several  deep  incisions  named  fissures  divide 
the  liver  into  five  parts  called  lobes.  The  falciform  or 
suspensory  ligament  which  is  a  fold  of  peritoneum  joins  the 
liver  to  the  diaphragm  and  extends  into  the  large  median 
fissure  known  as  the  umbilical  notch  because  during  fetal 
life  it  shelters  the  vein  leading  through  the  umbilical  cord 
to  receive  nourishment  from  the  mother. 

On  the  right  side  of  the  body  from  the  umbilical  notch 
is  the  large  right  median  lobe  enfolding  the  gall  bladder. 


FIG.  66.     LATERAL  ASPECT  OF  THE 
HEAD  WITH  THE  SKIN  REMOVED. 

cr,  Carotid  artery;  es,  esophagus; 
Im,  lymphatic  gland ;  nr,  vagus 
and  sympathetic  nerves;  sm, 
submaxillary  gland ;  tr,  trachea ; 
v,  cervical  vertebra. 


ORGANS    OF   DIGESTION.  123 

On  the  other  side  of  the  notch  is  a  small  left  median  lobe 
and  a  much  larger  left  lateral  lobe.  The  right  lateral  lobt 
is  dorsal  of  the  right  median  lobe,  and  is  divided  into  two 
parts  by  a  deep  cleft.  A  fifth  lobe  known  as  the  Spigelian 
or  caudate  lobe  is  a  small  triangular  portion  oi  the  liver 
connected  to  the  base  of  the  right  lateral  lobe  and  lying  be- 
tween the  neck  of  the  gall  bladder  and  the  end  of  the  stom- 
ach joining  the  esophagus. 

The  bile  secreted  by  the  liver  passes  through  the  several 
ducts  from  the  various  lobes,  to  the  main  hepatic  duct, 
which  may  be  seen  by  cutting  away  the  liver  from  the  right 
side  of  the  gall-cyst,  and  carefully  picking  off  the  perito- 
neum ensheathing  the  vessels  between  the  Spigelian  lobe 
and  the  cystic  duct.  The  latter  is  somewhat  convoluted  in 
its  course  from  the  deeply  imbedded  end  of  the  cyst,  to  a 
point  on  the  duodenum  about  three  centimeters  from  the 
pylorus.  The  main  hepatic  duct  joins  the  cystic  duct  (Fig. 
60)  near  its  middle.  The  common  duct  thus  formed  is 
known  as  the  common  bile  duct.  When  the  bile  is  secreted 
faster  than  it  is  permitted  to  enter  the  intestine,  it  passes 
backward  from  the  common  bile  duct  into  the  cyst. 

The  bile  aids  in  the  absorption  of  the  fats  by  the  villi, 
and  renders  the  chyme  alkaline.  The  formation  of  red 
blood-corpuscles  takes  place  in  the  liver  of  the  embryo, 
while  in  the  adult,  the  liver  destroys  these  corpuscles.  The 
chief  function  of  this  organ,  however,  is  the  formation  of 
glycogen  from  the  sugars  and  starches  eaten  and  the  gradual 
transformation  of  this  glycogen  into  sugar  as  demanded  for 
the  nutrition  of  the  body.  Diabetes  mellitus  is  caused  by  a 
diseased  liver  or  pancreas  which  permits  sugar  to  accumu- 
late in  the  blood. 

The  pancreas  (Fig.  60)  is  an  elongated  gland  bent  at 
a  right  angle  near  its  middle.  The  body  of  it  lies  dorsal 
to  the  pyloric  portion  of  the  stomach,  and  the  head  lies 


124  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

close  along  the  concavity  of  the  duodenum.  It  has  two 
ducts,  one  of  which  enters  the  duodenum  in  common  with 
the  common  bile  duct,  while  the  other  enters  about  three 
centimeters  further  caudad.  The  pancreatic  juice  acts  on 
the  starches,  proteids,  and  fats. 

THE  PERITONEUM. 

The  peritoneum  (Fig.  61)  is  the  serous  sac  lining  the 
abdominal  cavity  and  investing  most  of  the  organs  therein 
contained.  The  four  portions  of  the  peritoneum  are  known 
as  the  omenta,  the  mesenteries,  parietes,  and  ligaments. 

The  omenta  are  three  in  number,  the  largest  of  which  is 
the  great  or  gastrocolic  omentwn,  stretching  caudad  from 
the  dorsal  abdominal  wall  and  the  greater  curvature  of  the 
stomach,  so  as  to  cover  the  intestine  like  an  apron.  It  is 
composed  of  four  layers  of  peritoneum  forming  a  closed 
sac,  and  bearing  more  or  less  fat.  Two  layers  form  the 
ventral  wall  of  the  sac  attached  to  the  stomach,  and  two 
layers  are  also  present  in  the  dorsal  wall  of  the  sac  which 
invests  the  pancreas. 

The  lesser  omentum,  or  gastrohepatic  amentum,  extends 
caudad  from  the  liver  to  the  pyloric  part  of  the  stomach 
and  duodenum.  Its  two  folds  extend  from  the  two  sides 
of  the  portal  fissure,  ensheathing  the  portal  vein,  hepatic 
artery,  and  cystic  duct.  The  gastrosplenic  omen-turn  stretches 
from  the  cardiac  region  of  the  stomach  to  the  spleen,  which 
it  embraces,  and  then  proceeds  to  the  diaphragm. 

The  mesenteries  are  the  two  layers  of  peritoneum 
suspending  the  intestine  from  the  dorsal  abdominal  wall. 
There  are  four  mesenteries :  the  true  mesentery,  suspending 
the  jejunum  and  ileum ;  the  mesoduodenum,  suspending  the 
duodenum;  the  mesocolon,  suspending  the  colon;  and  the 
mesorectum,  suspending  the  rectum. 

The  parietes  or  parietal  peritoneum  is  that  portion  lining 


ORGANS    OF   DIGESTION.  125 

the  walls  of  the  abdominal  cavity.  It  is  a  closed  sac  in  the 
male,  but  in  the  female  the  Fallopian  tubes  open  into  it. 

The  ligaments  are  the  layers  of  the  peritoneum  suspend- 
ing other  organs  than  parts  of  the  alimentary  canal.  The 
suspensory  or  falciform  ligament  extends  from  the  caudal 
surface  of  the  diaphragm  and  the  abdominal  wall,  to  the  sur- 
face of  the  liver,  which  its  line  of  attachment  divides  into 
halves.  The  round  ligament  is  the  thickened  free  caudal 
border  of  the  suspensory  ligament.  It  is  the  remains  of  a 
vein  which  in  fetal  life  joined  the  offspring  to  the  mother. 
A  third  ligament  connects  the  dorsal  border  of  the  liver  with 
the  diaphragm.  The  broad  ligaments  of  the  uterus  are  the 
folds  of  peritoneum  which  embrace  the  uterus,  the  Fallo- 
pian tubes,  and  the  ovaries.  The  ovarian  ligaments  are 
short  cords  extending  from  the  ends  of  the  uterine  cornua 
to  the  ovaries.  The  round  ligaments  of  the  uterus  pass 
from  the  sides  of  the  uterus  to  the  brim  of  the  pelvis. 

The  peritoneum  is  called  a  serous  membrane  because  of 
the  colorless  serum  secreted  by  it.  Other  serous  membranes 
are  the  pericardium  of  the  heart,  the  pleura  lining  the  tho- 
racic cavity  and  investing  the  lungs,  and  the  synovial  mem- 
branes of  the  joints.  Serous  membranes  invest  only  such 
cavities  as  are  not  exposed  to  the  air.  All  other  cavities 
are  lined  by  mucous  membrane.  A  serous  membrane  con- 
sists of  a  layer  of  fibrous  connective  tissue  covered  by  plate- 
like  endothelial  cells. 


REMARKS    ON    THE   MAMMALIAN    DIGESTIVE    SYSTEM. 

The  digestive  system  of  mammals  varies  somewhat 
among  the  different  groups.  In  carnivorous  animals,  as  a 
rule,  the  alimentary  canal  is  much  shorter  than  in  herbivo- 
rous. In  the  wildcat  the  canal  is  four  times  the  length  of 
the  body,  while  the  canal  of  the  sheep  is  twenty  times  as 


126  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

long  as  the  body.  In  man  it  is  about  nine  times  as  long  as 
the  distance  from  the  crown  of  the  head  to  the  coccyx.  In 
Ruminants,  such  as  the  cow  and  the  sheep,  the  stomach  is 
very  large  and  divided  into  four  chambers — the  rumen  or 
paunch,  reticulum,  psalterium  or  manyplies,  and  abomasum 


FIG.  67.    DIAGRAM  OF  THE  STOMACH  OF  A  RUMINANT. 

a,  Dotted  line  showing  the  direction  of  the  food  in  the  process  of  diges- 
tion; abom,  abomasum;  du,  duodenum;  K,  esophagus;  ps,  psalter- 
ium; rt,  reticulum. 

(Fig.  67).  The  rumen  and  reticulum  serve  as  mere  storage 
cavities,  from  which  the  food  returns  to  the  mouth  for 
thorough  mastication,  and  then  passes  direct,  by  means  of 
a  groove  in  the  esophagus,  into  the  psalterium,  and  finally 
on  to  the  abomasum.  The  latter  is  the  true  stomach,  and 
is  provided  with  gastric  glands.  In  the  camels  the  rumen 
and  reticulum  have  connected  with  them  pouch-like  diver- 
ticula  for  the  storage  of  water.  The  constricted  openings 
of  the  pouches  into  the  rumen  or  reticulum  may  be  entirely 
closed  by  sphincter  muscles. 

In  man  and  the  higher  apes  there  is  present  an  attenuated 
extension  of  the  caecum  known  as  the  vermiform  appendix. 
In  the  fetus  of  man  it  is  proportionally  longer  than  in  the 
adult.  In  the  herbivorous  mammals,  such  as  the  cow  and 
rabbit,  the  caecum  is  greatly  enlarged,  so  as  to  play  an  im- 
portant part  in  digestion.  In  a  few  forms,  such  as  the 
sloths,  some  Cetacea,  and  a  few  Carnivora,  the  caecum  is 
absent. 

The  lowest  mammals,  the  Monotremata,  resemble  birds 


ORGANS    OF   DIGESTION.  127 

and  reptiles  in  possessing  a  cloaca  into  which  open  the 
rectum  and  the  urinary  and  genital  ducts.  The  cloaca 
opens  externally  through  the  anus.  Salivary  and  thyroid 
glands,  pancreas,  and  liver  are  present  in  all  mammals,  but 
the  gall-cyst  is  absent  in  Cetacea,  the  Perissodactyla,  Hyra- 
coidea,  and  a  few  Rodentia.  The  liver  is  usually  relatively 
larger  in  fat-eating  animals. 

PRACTICAL   QUESTIONS    AND    SUGGESTIONS. 

1.  Describe  the  fauces. 

2.  Describe  in  detail  every  feature  visible  on  the  dorsal  surface  of 
the  tongue. 

3.  Give  the  number  of  fangs  in  each  tooth  of  the  permanent  set. 

4.  Give  the  number  of  each  kind  of  teeth  in  the  two  sets. 

5.  Draw  two  aspects  of  the  sectorial  tooth. 

6.  How  thick  is  the  enamel  of  the  teeth? 

7.  Name  some  mammals  which  do  not  have  enamel  on  the  teeth. 

8.  Name  some  toothless  mammals. 

9.  Name  some  mammals  having  only  one  set  of  teeth. 

10.  Give  the  dental  formulae  for  three  ungulates. 

11.  In  what  animals  are  some  of  the  teeth  greatly  enlarged? 

12.  Do  any  ruminants  have  upper  incisors? 

13.  Name  the  important  features  of  the  pharynx. 

14.  Name  every  organ  in  the  abdominal  cavity,   telling  with  what 
other  organs  it  is  in  contact. 

15.  Describe  as  much  of  the  peritoneum  as  you  can  see  in  your 
specimen. 

\yi6.  Draw  the  alimentary  canal  in  its  natural  position,  showing  all 
ducts  leading  into  it,  and  label  all  parts. 

17.  How  much  longer  is  the  small  intestine  than  the  large  one? 

18.  On  what  does  the  length  of  the  canal   in   different  mammals 
largely  depend? 

V 19.  Make  a  section  of  a  portion  of  the  wall  of  the  stomach  and  draw 
what  is  seen,  labelling  all  parts. 

V  20.  Make  a  section  of  the  small  intestine,  draw  what  can  be  seen  by 
naked  eye  or  simple  microscope. 

21.  About  how  many  villi  to  each  square  millimeter? 

22.  Describe  the  two  channels  through  which  the  food  passes  from 
ihe  intestines  to  the  heart. 

23.  Make  a  somewhat  diagrammatic  drawing  representing  that  part 
of  the  venous  system  conveying  the  food  from  the  intestines  to  the  heart. 


128  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

24.  What  is  the  size  of  the  caecum  in  other  mammals  than  the  cat? 

25.  Give  the  location,  size,  and  form  of  the  salivary  glands. 

26.  Name  the  lobes  of  the  liver  in  order  of  their  size. 

27.  How  is  the  liver  held  in  place? 

Draw  the  pancreas,  showing  ducts  leading  to  the  intestine. 

29.  Draw  the  complex   stomach  characteristic  of  many  ruminants. 

30.  What  is  the  cloaca  and  in  what  mammals  is  it  present? 


THE  VASCULAR  SYSTEM. 

The  vascular  system  is  composed  of  the  central  forcing 
muscular  organ,  the  heart ;  a  system  of  vessels,  the  arteries, 
carrying  the  blood  from  the  ventricles  to  the  lungs  and  all 
parts  of  the  body;  a  system  of  vessels,  the  veins,  returning 
the  blood  to  the  auricles ;  and  numerous  microscopic  vessels, 
the  capillaries,  connecting  the  termination  of  the  arteries 
with  the  origin  of  the  veins. 

THE  HEART. 

The  location  of  the  heart  in  the  cat  may  be  seen  by  re- 
moving the  ventral  thoracic  wall,  but  for  the  study  of  the 
parts,  the  heart  of  an  ox  or  a  sheep  will  be  found  more 
satisfactory.  The  heart  of  the  cat  lies  between  the  lungs 
(Fig.  82)  in  the  thoracic  cavity  a  little  to  the  left  of  the 
median  line.  The  caudal  end  is  the  apex,  and  the  cranial 
end  is  the  base.  The  entire  organ  is  invested  by  a  tough 
membrane,  the  pericardium,  which  when  cut  permits  the 
pericardial  fluid  to  run  out.  All  the  blood-vessels  originate 
from  the  dorsocranial  aspect  of  the  heart. 

It  is  composed  of  a  right  and  left  half,  each  of  which 
consists  of  an  auricle  and  a  ventricle.  The  separation  be- 
tween the  two  halves  is  apparent  on  the  ventral  surface. 
The  auricles  receive  the  blood  from  the  veins  and  pass  it 
to  the  ventricles,  which  disperse  it  through  the  arteries. 
There  is  no  aperture  between  the  auricles  or  the  ventricles. 
The  aperture  between  the  right  auricle  and  the  right  ven- 
tricle is  guarded  by  the  tricuspid  valve  which  prevents  the 
blood  from  returning  into  the  auricle  when  the  systole  or 
contraction  pushes  the  blood  into  the  pulmonary  artery. 

129 


1 3o 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


The  opening  between  the  left  -auricle  and  the  left  ventricle 
is  guarded  by  the  bicuspid  or  mitral  valve.     These  valves 


FIG.  68.  PHOTOGRAPH  OF  THE  VEN- 
TRAL ASPECT  OF  THE  HUMAN 
HEART  INJECTED. 

a,  aorta ;  b,  left  ventricle ;  c,  carotid 
arteries ;  d,  right  auricle ;  e, 
esophagus;  /,  left  auricle;  n, 
right  auricle;  s,  subclavian  ar- 
tery; t,  trachea;  v,  superior 
vena  cava.  J  natural  size. 


FIG.  69.  HEART  VIEWED  VEN- 
TRALLY,  WITH  VENTRAL  HALF  OF 
THE  AURICLES  AND  VENTRICLES 
CUT  AWAY  AND  THE  AURICLES 
DRAWN  LATERAD.  Partly  dia- 
grammatic. 

a,  Orifice  of  the  aorta ;  ao,  aorta ; 
aao,  arch  of  the  aorta ;  ap,  orifice 
of  the  precava ;  as,  orifice  of  the 
postcava;  Iv,  left  pulmonary 
veins ;  Ivn,  left  ventricle ;  mt, 
mitral  or  bicuspid  valve ;  la,  left 
auricle;  p,  orifice  of  the  pulmon- 
ary veins;  pc,  inferior  vena 
cava;  prc,  superior  vena  cava; 
ba,  orifice  of  the  pulmonary 
artery;  prv,  right  pulmonary 
veins ;  rv,  right  ventricle  and 
one  of  the  right  pulmonary 
veins ;  ra,  right  auricle ;  rp,  right 
pulmonary  artery ;  tr,  tricuspid 
valve;  xp,  left  pulmonary  artery. 


may  be  displayed  by  cutting  away  the  caudal  half  of  the 
ventral  wall  of  the  ventricles,  when  the  chorda  tendinea, 
delicate  tendinous  cords,  will  be  seen  extending  from  the 


THE   VASCULAR    SYSTEM. 


margins  of  the  translucent  membranous  valves  to  the 
columnar  carnese  or  muscular  projections  on  the  walls  of 
the  ventricles.  The  walls  of  the  auricles  are  thin  in  com- 
parison with  the  walls  of  the  left  ventricle,  which  are  twice 
as  thick  as  the  walls  of  the  right  ventricle  (Fig.  70). 

The  auricles  are  very  small  when  not  injected,  and  may 


rs 


fie 


FIG.  70.  VENTRAL  ASPECT  OF  THE 
HEART  WITH  ITS  CAUDAL  THIRD 
CUT  OFF  TRANSVERSELY. 

a,  Adipose  tissue;  be,  innominate 
artery;  la,  left  auricle;  }v,  left 
ventricle ;  Ic,  left  carotid  artery ; 
o,  ductus  arteriosus ;  pv,  pul- 
monary vein ;  ba,  pulmonary 
artery;  pc,  superior  vena  cava; 
psc,  inferior  vena  cava;  ra, 
right  auricle;  re,  right  carotid 
artery;  rs,  right  subclavian 
artery ;  rv,  right  ventricle ;  sb, 
left  subclavian  artery;  tr,  tra- 
chea. 


FIG.   71.     DORSAL  ASPECT  OF  THE 
HEART  OF  THE  CAT. 

ao,  Aorta;  ap,  apex;  as,  azygos 
vein;  be,  innominate  artery; 
ca,  coronary  artery ;  cv,  coro- 
nary vein;  /_, -left  auricle;  Ic, 
left  carotid  artery ;  Isb,  left  sub- 
clavian  artery;  p,  inferior  vena 
cava;  pc,  superior  vena  caya; 
pa,  pulmonary  artery  dividing 
into  its  right  and  left  branches ; 
ra,  right  auricle;  re,  right  ca- 
rotid ;  rs,  right  subclavian ;  v, 
pulmonary  veins. 


by  the  beginner  be  cut  away  with  the  pericardium  and  sur- 
rounding adipose  tissue.  The  right  auricle  receives  three 
veins,  the  superior  vena  cava,  inferior  vena  cava  and  coro- 
nary veins,  all  of  which  enter  its  dorsal  aspect.  The  portion 


i32  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

of  the  auricle  into  which  the  above  veins  open  is  the  sinus 
venosus.  At  the  dorsal  part  of  the  septum  which  divides 
this  auricle  from  the  adjoining  one  is  an  oval  depression, 
the  fossa  ovalis,  where,  in  the  embryo,  the  two  auricles  com- 
municated. The  left  auricle  is  in  contact  with  the  right 
dorsally,  and  receives  three  pulmonary  veins  (Fig.  71). 

From  the  right  ventricle  arises  the  pulmonary  artery 
which  carries  the  impure  blood  to  both  lungs.  Its  mouth 
is  guarded  by  three  semilunar  valves  which  prevent  the  re- 
turn of  the  blood.  The  left  ventricle  gives  origin  to  only 
one  important  vessel,  the  aorta,  which  arches  dorsally 
around  the  left  auricle,  and  at  the  apex  of  the  arch  gives 
off  two  branches,  the  innominate,  and  the  left  subclavian. 
Three  semilunar  valves  also  guard  the  mouth  of  the  aorta. 
The  arteries  of  the  heart  may  easily  be  distinguished  from 
the  veins  by  the  fact  that  the  walls  of  the  former  are  much 
thicker. 

THE  ARTERIES  OF  THE  TRUNK. 

The  blood-vessels  form  two  systems  of  circulation;  the 
one  known  as  the  pulmonary  circulation  includes  the  arteries 
carrying  blood  from  the  right  ventricle  to  the  lungs,  and  the 
veins  returning  the  blood  from  the  lungs  to  the  left  auricle; 
the  other,  known  as  the  systemic  circulation,  includes  the 
arteries  conveying  the  blood  from  the  left  ventricle  to  all 
parts  of  the  body,  and  the  veins  returning  the  blood  to  the 
right  auricle. 

The  main  artery  of  the  systemic  circulation  is  the  aorta, 
which,  beginning  in  the  left  ventricle,  arches  dorsad  to  the 
heart  and  extends  along  the  spinal  column  to  the  tail.  That 
portion  in  the  thoracic  cavity  is  termed  the  thoracic  aorta, 
while  that  portion  in  the  abdominal  cavity  is  the  abdominal 
aorta.  Three  semilunar  valves  guard  the  mouth  of  the 
aorta  at  its  opening  from  the  ventricle,  in  order  that  the 


THE   VASCULAR    SYSTEM. 


133 


blood  may  not  be  forced  back  into  the  heart  by  the  con- 
traction of  the  muscular  coat  of  the  arteries* 

The  branches  of  the  thoracic  aorta  are  as  follows :  the 
right  and  left  coronary,  arising  from  the  aorta  immediately 
beyond  its  exit  from  the  ventricle,  are  distributed  to  the 
walls  of  the  heart.  From  the  arch  of  the  aorta  arise 
two  large  branches;  first,  the  innominate,  giving  origin  to 
the  right  subclavian  supplying  blood  to  the  arm,  and  the 
right  and  left  carotids  supply- 
ing the  head  and  neck;  and 
second,  the  left  subclavian,  sup- 
plying the  left  arm,  brain,  and 
sternum  (Fig.  72).  Ten  pairs 
of  intercostal  arteries  supply 
the  intercostal  spaces,  muscles, 
of  the  back,  and  the  spinal  cord. 
Two  bronchial  arteries  go  to 
the  lung  tissue.  Two  to  four 
esophageal  arteries  are  distrib- 
uted to  the  esophagus.  Two 
or  three  pairs  of  lumbar  ar- 
teries pierce  the  muscles  of  the 
back. 

FIG.    72.      CHIEF    ARTERIES    OF    THE 
TRUNK,  VENTRAL  ASPECT. 

ar,  Arch  of  the  aorta;  be,  innomi- 
nate; ce,  cceliac  axis;  cd,  cau- 
dal; e,  gastric;  /,  gastric;  gr, 
gastric ;  gas,  gastroduodenalis ;  hp, 
hepatic ;  ht,  location  of  heart ;  ten, 
intercostals ;  ic,  external  iliac ;  it, 
internal  iliac ;  il,  iliolumbar ;  im, 
inferior  mesenteric;  Is,  left  sub- 
clavian; //>/,  left  pulmonary;  m, 
splenic ;  o,  splenic ;  r,  right  pul- 
monary; re,  renal;  sp,  splenic 
trunk;  sms,  superior  mesenteric; 
sm,  spermatic  or  ovarian;  s,  ad- 
renolumbalis ;  i,  2,  3,  4,  5,  and  6, 
lumbar  arteries. 


134  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

The  abdominal  aorta  gives  off  the  following  branches: 
the  coeliac  axis,  the  superior  mesenteric,  the  adrenolumbalis, 
a  pair  of  renal,  a  pair  of  genital,  an  inferior  mesenteric,  a 
pair  of  iliolumbar,  seven  or  eight  pairs  of  lumbar,  a  pair 
of  external  iliacs,  a  pair  of  internal  iliacs,  and  a  caudal 
artery  (Fig.  72). 

The  coeliac  axis  is  a  large  branch  arising  just  caudad  to 
the  diaphragm  and  gives  off  the  hepatic  branch  to  the  liver, 
pancreas,  and  duodenum,  the  gastric  to  the  stomach,  and 
is  continued  as  the  splenic,  supplying  the  pancreas  and  the 
spleen.  The  phrenic  artery,  supplying  the  diaphragm, 
sometimes  arises  from  the  coeliac  axis,  but  usually  from  the 
adrenolumbalis. 

The  superior  mesenteric  is  about  the  same  size  as  the 
coeliac  axis,  and  arises  within  one  centimeter  caudad.  It 
sends  branches  to  the  pancreas  and  both  intestines.  The 
adrenolumbalis  is  a  small  branch  on  the  left  side  dividing 
into  the  adrenal,  phrenic,  and  muscular.  The  renal  arteries 
supply  the  kidneys  and  usually  the  suprarenal  bodies.  The 
genital  arteries  are  small,  and  arise  from  one  to  two  centi- 
meters caudad  of  the  renal  arteries.  They  pass  obliquely 
caudad  to  the  ovaries  in  the  female,  and  the  testes  in  the 
male.  The  inferior  mesenteric  is  almost  as  large  as  the 
superior  mesenteric.  It  is  distributed  to  the  large  intestine. 
The  pair  of  iliolumbar  arteries  are  small  branches  supply- 
ing the  muscles  of  the  iliac  region. 

Four  or  five  pairs  of  lumbar  arteries  are  given  off  from 
the  dorsal  side  of  the  aorta  at  regular  intervals  between 
the  diaphragm  and  the  origin  of  the  external  iliac  arteries. 
They  supply  the  muscles  of  the  back  and  spinal  cord.  The 
external  iliac  arteries  are  the  largest  branches  of  the  ab- 
dominal aorta  and  carry  blood  to  the  hind-limbs.  The 
internal  iliac  arteries  arise  more  than  a  centimeter  caudad 
to  the  external  iliacs  and  furnish  blood  to  the  pelvic  viscera 


THE   VASCULAR    SYSTEM.  135 

and  the  muscles  of  the  innominate  region.  The  caudal 
artery  is  the  continuation  of  the  aorta  beyond  the  origin  of 
the  internal  iliacs.  It  extends  into  the  tail  (Fig.  72). 

ARTERIES  OF  THE  HEAD  AND  NECK. 

From  the  arch  of  the  aorta  arise  the  innominate  and 
left  subclavian,  which  supply  the  sternum,  neck,  head,  and 
anterior  extremities  with  blood.  The  innominate  gives  off 
the  left  carotid  and  then  divides  into  the  right  carotid 
and  right  subclavian  (Fig.  73).  Sometimes  the  two  caro- 
tids arise  as  a  single  trunk  from  the  innominate,  which  is 
then  continued  as  the  right  subclavian.  In  this  case  the 
common  trunk  of  the  carotid  usually  bifurcates  within  one 
or  two  centimeters  of  its  origin,  forming  the  right  common 
carotid  and  the  left  common  carotid,  lying  on  the  respective 
sides  of  the  trachea  beneath  the  sternomastoid  and  the 
sternohyoid  muscles.  The  vagus  or  tenth  cranial  nerve  and 
the  sympathetic  trunk  lie  in  the  same  sheath  with  the  caro- 
tid (Fig.  66). 

Each  carotid  artery  in  the  neck  region  gives  off  the  fol- 
lowing branches :  a  thyroid  to  the  thyroid  cartilage  and 
gland,  and  a  muscular  to  the  muscles  of  the  neck.  At  the 
base  of  the  skull,  about  the  middle  of  the  bulla  of  the  tem- 
poral bone,  a  slight  enlargement  of  the  vessel  is  seen,  from 
which  arises  the  very  small  internal  carotid,  leading  through 
the  foramen  lacerum  medius  to  the  base  of  the  brain,  where 
it  joins  the  circle  of  Willis.  The  continuation  of  the  com- 
mon carotid  is  now  known  as  the  external  carotid.  This, 
after  giving  off  a  lingual  branch  to  the  tongue,  an  external 
maxillary  branch  to  the  lower  jaw,  a  post-auricular  branch, 
and  a  temporal  branch,  turns  to  pass  along  the  medial 
aspect  of  the  mandible,  where  it  is  named  the  internal 
maxillary,  whose  main  branches  are  the  inferior  alveolar, 
the  middle  meningeal  supplying  the  dura  mater,  several 


i36 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


branches  to  form  the  carotid  plexus,  a  palatine,  spheno pala- 
tine, and  infraorbital  The  latter  is  the  direct  continuation 
of  the  internal  maxillary.  It  supplies  the  upper  teeth,  lower 
eyelid,  parts  of  the  nose,  and  upper  lip.  An  ophthalmic 
branch,  supplying  structures  in  the  orbit,  may  arise  from 
the  carotid  plexus  or  the  internal  maxillary. 


FIG.  73.     VENTRAL  ASPECT  OF  THE  ARTERIES  OF  THE  HEAD  AND  NECK. 
The  carotids  with  their  branches  have  been  drawn  laterad. 

a,  Internal  maxillary;  ac,  anterior  cerebellar;  ce,  median  cerebral;  cr, 
posterior  cerebral ;  cp,  posterior  cerebellar ;  ex,  carotid  plexus,  many 
of  whose  branches  reunite  in  one,  ex' ,  which  is  cut  off ;  ex,  external 
carotid ;  em,  external  maxillary ;  inc,  origin  of  internal  carotid ;  inc', 
union  of  internal  carotid  with  circle  of  Willis;  ia,  inferior  alveolar; 
if,  infraorbital;  i,  optic  chiasma;  li,  lingual;  mm,  middle  meningeal; 
ms,  muscular;  oc,  occipital;  ol,  anterior  cerebral;  pi,  palatine;  pa, 
posterior  auricular;  s,  anterior  spinal;  th,  thyroid;  x,  hypophysis; 
i,  2,  3,  4,  5,  and  6,  transverse  foramina  in  cervical  vertebrae. 


THE   VASCULAR   SYSTEM.  137 

The  vertebral  artery  is  the  first  branch  given  off  by  either 
subclavian.  It  proceeds  dorsad  and  craniad  to  the  sixth- 
cervical  vertebra,  whence  it  extends  through  the  transverse 
foramina  of  the  cervical  vertebrae  and  foramen  magnum,  to 
a  junction  with  its  fellow  in  the  median  line  on  the  ventral 
aspect  of  the  medulla  oblongata.  The  union  of  the  two 
vertebral  arteries  forms  the  basilar  artery,  which,  after  giv- 
ing off  several  branches  to  the  medulla  and  cerebellum, 
divides  craniad  of  the  pons  Varolii,  forming  the  circle  of 
Willis  around  the  infundibulum  and  the  optic  chiasma  at 
the  base  of  the  brain.  The  circle  of  Willis  receives  the  in- 
ternal carotid  and  gives  off  several  arteries  to  the  cerebrum. 
In  man  the  internal  carotid  is  much  larger  proportionately 
than  in  the  cat  (Fig.  73). 

THE  ARTERIES  OF  THE  THORACIC  LIMB. 

There  is  more  or  less  variation  in  the  branching  of  the 
arteries  in  the  limbs.  No  two  cats  are  found  exactly  alike 
as  to  their  arteries  or  veins.  The  same  is  true  of  all  other 
mammals. 

The  subclavian  artery,  which  on  the  right  side  springs 
from,  or  is  merely  a  continuation  of,  the  innominate  and 
on  the  left  side  arises  from  the  arch  of  the  aorta,  sup- 
plies the  forelimbs  with  blood  (Figs.  73  and  74).  When 
the  subclavian  reaches  the  armpit,  it  is  called  the  axillary 
artery,  and  its  continuation  along  the  humerus  is  the 
brachial  artery.  A  continuation  of  the  same  artery  along 
the  radius  is  the  radial  artery,  furnishing  a  large  part  of  the 
blood  to  the  fingers. 

Four  branches  arise  from  the  subclavian :  the  vertebral 
artery,  extending  to  the  brain  through  the  transverse  for- 
amina of  the  cervical  vertebrae;  the  internal  mammary 
artery,  arising  from  the  ventral  side  of  the  subclavian  op- 
13 


133 


ELEMENTS   OF   MAMMALIAN   ANATOMY. 


posite  the  origin  of  the  vertebral,  and  extending  along  the 
visceral  surface  of  the  sternum,  and  sometimes  supplying 
the  pericardium  of  the  heart;  the  superior  intercostal,  aris- 
ing near  the  vertebral  artery  and  supplying  the  first  and 
second  intercostal  spaces,  the  deep  muscles  of  the  back,  and 
the  serratus  magnus;  and  the  thyroid  axis,  extending 
craniad  to  supply  some  muscles  of  the  neck  and  the  lateral 
aspect  of  the  scapula  (Fig.  74). 

The  axillary  artery  gives  origin  to  three  branches :  the 
anterior  thoracic,  the  long  thoracic,  and  the  circumflex. 
The  anterior  thoracic  supplies  the  pectoral  muscles.  The 

long  thoracic  is  distributed  chiefly 
to  the  latissimus  dorsi.  The  cir- 
cumflex artery  is  .almost  as  large 
as  the  continuation  of  the  axillary, 
which  beyond  this  point  is  called 
the  brachial.  The  circumflex, 
about  a  centimeter  from  its  ori- 
gin, after  giving  off  the  subscapu- 
lar,  which  is  distributed  mainly  to 


FIG.   74. 


ARTERIES    OF   THE    FORELIMB. 
VENTRAL  ASPECT. 


a,  Digital  artery;  an,  anastomotica 
magna;  ac,  anterior  circumflex;  ai, 
anterior  interosseous ;  ax,  axillary ;  at, 
anterior  thoracic;  b,  digital  artery;  be, 
innominate ;  br,  brachial ;  c,  dorsal 
branch  of  the  radial  where  it  passes 
between  the  second  and  third  meta- 
carpals  to  the  palmar  side ;  ex,  circum- 
flex ;  is,  superior  intercostal ;  Is,  left 
subclavian;  It,  long  thoracic;  m, 
branch  to  extensor  muscles;  nt,  nutri- 
ent ;  pi,  posterior  interosseous ;  r, 
radial;  rd,  radial  recurrent;  sf,  supra- 
condyloid  foramen  of  the  humerus; 
spr,  superior  profunda ;  sb,  subscapu- 
laris;  sp,  suprascapularis ;  st,  sternal; 
th,  thyroid  axis;  ul,  ulnar;  ur,  ulnar 
recurrent ;  vt,  vertebral. . 


THE   VASCULAR   SYSTEM.  139 

structures  in  the  subscapular  fossa,  winds  around  the  neck 
of  the  humerus  to  its  distribution  in  the  triceps  and  deltoid 
muscles. 

The  brachial  artery,  in  addition  to  several  muscular 
branches,  gives  origin  to  the  anterior  circumflex,  superior 
profunda,  the  nutrient,  and  anastomotica  magna.  The  an- 
terior circumflex  supplies  the  biceps  and  head  of  the  hu- 
merus. The  superior  profunda  is  distributed  to  the  muscles 
on  the  caudal  aspect  of  the  humerus.  The  nutrient  artery 
enters  the  nutrient  foramen  of  the  humerus.  The  anasto- 
motica magna  is  the  small  branch  supplying  the  convexity 
of  the  elbow.  The  brachial  artery  after  passing  through 
the  supracondyloid  foramen  takes  the  name  of  radial. 

The  radial  artery,  which  lies  deep  beneath  the  flexor 
muscles  on  the  caudal  aspect  of  the  proximal  half  of  the 
radius  (Fig.  74),  becomes  superficial  along  its  distal  half, 
where  the  vessel  is  covered  by  skin  and  fascia  only.  In  the 
region  of  the  wrist,  it  curves  dorsad  and  then  pierces  be- 
tween the  second  and  third  metacarpals  to  the  palmar  side, 
where  it  sends  branches  to  each  of  the  digits,  and  forms 
the  palmar  arch  by  anastomosing  with  the  ulnar  artery  be- 
neath the  flexor  muscles.  In  addition  to  a  few  small 
branches,  the  radial  gives  off  the  following:  the  radial  re- 
currens,  supplying  the  concavity  of  the  elbow;  the  ulnar 
recurrens,  supplying  the  convexity  of  the  elbow;  the  poste- 
rior inter  osseous,  passing  caudad  between  the  radius  and 
the  ulna  to  the  extensor  muscles;  the  anterior  interosseous, 
passing  along  the  cranial  side  of  the  interosseous  mem- 
brane; the  ulnar,  extending  beneath  the  flexor  muscles, 
which  it  supplies,  to  the  palm,  where  it  anastomoses  with 
the  radial  to  form  the  palmar  arch;  and  the  volar  branch, 
supplying  the  superficial  palmar  region.  The  ul-nar  and 
anterior  interosseous  frequently  arise  from  the  same  trunk, 
as  shown  in  the  figure.  The  ulnar  artery  in  the  cat  is  so 


140 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


small  that  it  is  frequently  not  filled  by  the  starch  injection, 
but  in  man  it  is  larger  than  the  radial. 

THE  ARTERIES  OF  THE  HIND-LIMB. 

As  in  the  forelimb,  the  branching  of  the  arteries  in  the 
hind-limb  varies  considerably  in  different  specimens.  The 
main  artery  of  the  leg  lies  on  the  ventral  or  medial  aspect 
of  the  femur,  passing  obliquely  to  the  caudal  side  of  the 
knee-joint,  where  it  divides  into  two  branches  (Fig.  75), 
one  extending  along  the  cranial,  the  other  along  the  caudal 


FIG.  75.    ARTERIES  OF  THE  RIGHT  LEG.     VENTRAL  ASPECT. 

a,  Aorta;  at,  anterior  tibial;  af,  anterior  femoral;  cd,  caudal;  eg,  epi- 
gastric; em,  external  malleolar;  fern,  femoral;  im,  internal  mal- 
leolar ;  il,  external  iliac;  it,  internal  iliac;  lu,  iliolumbar;  m,  digital; 
n,  digital;  o,  digital;  p,  peroneal ;  pa,  profunda;.  pf,  posterior  supe- 
rior femoral;  pi,  posterior  inferior  femoral;  pn,  plantar;  pp, 
popliteal;  pt,  posterior  tibial;  ps,  saphenous. 

aspect  of  the  crus.    The  cat,  or  at  least  the  caudal  half  of  a 
cat,  should  be  fastened  to  the  dissecting  tray  on  its  back, 


THE   VASCULAR    SYSTEM.  Hr 

the  abdominal  wall  removed,  and  the  viscera  pushed  laterad 
to  demonstrate  the  origin  of  the  artery  of  this  limb.  As 
in  the  forelimb,  the  main  artery  in  different  portions  of  the 
leg  takes  the  name  of  the  corresponding  region. 

The  external  iliac  is  the  largest  artery  arising  from  the 
aorta  in  the  lumbar  region.  It  gives  off  but  one  important 
branch,  the  prof  undo,,  which,  extending  caudad,  soon  gives 
off  a  large  epigastric  artery  to  the  abdominal  wall,  then 
smaller  branches  to  the  external  genital  organs,  and  numer- 
ous branches  to  the  muscles  on  the  caudal  aspect  of  the 
femur. 

The  femoral  artery,  which  is. a  continuation  of  the  ex- 
ternal iliac,  extends  along  the  medial  aspect  of  the  femur. 
In  the  proximal  half  of  its  course  it  is  quite  superficial,  but 
the  distal  portion  is  covered  by  the  gracilis,  sartorius,  and 
semimembranosus  muscles.  It  furnishes  four  important 
branches :  the  anterior  femoral,  supplying  mainly  the  qua- 
driceps extensor  muscle;  the  superior  posterior  femoral, 
supplying  the  adductor  and  hamstring  muscles;  the  saphe- 
nous,  accompanying  the  saphenous  nerve  and  vein  to  the 
foot,  where  it  branches  and  anastomoses  with  the  plantar 
artery ;  and  the  posterior  inferior  femoral,  supplying  mainly 
the  gastrocnemius  group  of  muscles  (Fig.  52). 

The  popliteal  artery  is  the  continuation  of  the  femoral 
artery  in  the  popliteal  region  on  the  caudal  aspect  of  the 
knee-joint.  One  or  two  articular  branches  are  given  off 
here  to  the  joint,  in  addition  to  the  posterior  tibial,  which 
supplies  the  deep  muscles  of  the  crus. 

The  anterior  tibial  artery  is  the  continuation  of  the  pop- 
liteal on  the  lateral  cranial  aspect  of  the  tibia,  adjacent  to 
the  bone.  By  separating  the  tibialis  anticus  and  extensor 
longus  digitorum  muscles,  this  artery  is  well  displayed. 
Near  the  knee-joint  a  small  branch,  the  peroneal,  is  given 
off,  and  passes  to  the  dorsal  aspect  of  the  foot,  where  it 


142 


ELEMENTS   OF   MAMMALIAN   ANATOMY. 


anastomoses  with  the  dorsal  branch  of  the  saphenous,  form- 
ing a  superficial  arch  sending  branches  to  the  digitis.  The 
peroneal  is  so  small  that  it  is  frequently  not  injected.  In 
the  tarsal  region  two  branches,  an  external  malleolar  and 
an  internal  malleolar,  are  given  off.  A  centimeter  or  two 
distal  to  the  latter  branch,  the  main  artery  passes  between 

the  second  and  third  meta- 
tarsals  to  the  deep  plantar 
region,  where  it  receives  an 
anastomosing  branch  from 
the  saphenous,  and  sends 
off  branches  to  the  digits. 

THE  VENOUS  SYSTEM 

The  veins  are  the  vessels 
returning  the  blood  to  the 
heart.  As  a  rule,  veins  carry 
only  impure  blood,  but  the 
pulmonary  veins  returning 
blood  from  the  lungs  to 
the  left  auricle  carry  pure 
blood.  After  death  the 
veins  can  readily  be  distin- 
guished from  the  arteries  by 
the  fact  that  they  have  much 
thinner  walls  than  the  ar- 
teries and  are  usually  full  of 
blood,  while  the  arteries  are 
empty  (Fig.  76).  This  is 
due  to  the  fact  that  the  thick 
muscular  coat  of  the  arteries,  by  its  contraction  tends  to 
drive  the  blood  into  the  veins,  whose  muscular  coat  is  very 
thin.  The  three  coats  composing  the  walls  of  the  veins  are 
the  epithelial,  or  tunica  intima;  the  middle,  or  muscular; 


FIG.  76.  CROSS-SECTION  OF  AR- 
TERY AND  VEIN.  X  350. 

V ',  Vein  ;  A,  artery ;  en,  inner  coat ; 
ep,  epithelium  lining  the  vessels ; 
et,  middle  or  muscular  coat  of 
vein;  ex,  muscular  coat  of  ar- 
tery; fb,  fibro-areolar  coat. — 
(From  Martin's  "Human 
Body."} 


THE  VASCULAR   SYSTEM.  H3 

and  the  tunica  adventitia,  or  outer  elastic  coat  of  fibro-areo- 
lar  tissue.  The  veins  of  the  central  nervous  system  and  its. 
membranes  have  no  muscular  coat.  While  the  only  valves 
in  the  arteries  are  found  at  their  origin  from  the  heart,  the 
veins  of  the  limbs,  neck,  and  the  head  possess  numerous 
valves.  These  valves  are  formed  by  semilunar  folds  of  the 
epithelial  coat,  strengthened  by  fibrous  tissue  (Fig.  77). 

The  main  deep  veins  of  the  limbs  accompany  the  arteries 
and  take  the  same  names  as  the  arteries.  A  superficial  set 
of  veins  is  present  also  in  the  limbs.  The  large  superficial 
vein  on  the  lateral  aspect  of  the  forelimb  is  the  cephalic. 
The  superficial  vein  extending  along  the 
medial  aspect  of  the  hind-limb  is  the 
saphenous. 

The  Veins  of  the  Trunk,  Head,  and 
Neck.  —  There  are  two  chief  venous 
trunks:  the  precava,  or  superior  vena 
cava,  and  the  postcava,  or  inferior  vena 
cava.  Both  vessels  open  into  the  dorsal 
aspect  of  the  right  auricle.  The  veins 
received  by  the  inferior  vena  cava  are  SHOWS  THE  Di- 
thirteen  in  number.  The  phrenic  veins  N 


collect  the  blood  from  the  diaphragm  and  v,  Semilunar  val- 
empty  into  the  vena  cava  immediately  of  S  the  valve.  g6 
caudad  of  the  diaphragm.  The  several 
hepatic  veins  collect  the  blood  from  the  liver,  which  must  be 
partly  dissected  away  to  see  their  entrance  into  the  vena 
cava.  The  two  suprarenal  veins  return  the  blood  from  the 
suprarenal  bodies  and  two  renal  veins  carry  the  blood  from 
the  kidneys.  The  left  ovarian  or  spermatic  vein  is  a  tribu- 
tary to  the  left  renal,  but  the  right  ovarian  empties  directly 
into  the  vena  cava.  A  pair  of  small  iliolumbar  veins  col- 
lecting blood  from  the  lumbar  muscles  empty  into  the  vena 
cava  a  centimeter  or  more  craniad  to  the  large  common 


r44  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

iliacs.  The  union  of  the  common  iliac  veins  collecting  the 
blood  from  the  hind-limbs  and  the  pelvic  region,  and  the 
caudal  vein,  forms  the  beginning  of  the  inferior  vena  cava. 
The  common  iliac  is  formed  by  the  union  of  the  external 
and  internal  iliac  veins  in  the  pelvis.  The  former  is  much 
the  larger  of  the  two. 

The  portal  system  begins  with  the  veins  collecting  the 
blood  from  the  intestines,  pancreas,  spleen,  and  stomach, 
and  terminates  where  the  hepatic  veins  enter  the  vena  cava. 
The  inferior  mesenteric  vein  collects  the  blood  from  the 
large  intestine;  the  superior  mesenteric,  from  the  small  in- 
testines; the  gastrosplenic,  from  the  spleen,  stomach,  and 
pancreas;  the  coronary,  from  the  lesser  curvature  of  the 
stomach;  the  gastro-epiploica,  from  the  greater  curvature 
of  the  stomach;  and  the  pancreatoduodenalis,  from  the  pan- 
creas and  duodenum.  The  last  three  may  empty  directly 
into  the  portal  vein  or  into  one  of  the  three  branches  first 
named  (Fig.  78). 

The  superior  vena  cava  extends  from  the  union  of  the 
innominate  veins  to  the  right  auricle.  Three  important  veins 
empty  into  the  superior  vena  cava :  the  azygos,  collecting 
blood  from  the  intercostal  spaces;  the  sternal,  lying  on  the 
visceral  surface  of  the  sternum;  and  the  right  vertebral, 
which,  with  its  fellow,  collects  the  blood  from  the  deep 
muscles  and  spinal  cord  in  the  region  of  the  atlas,  and  after 
making  a  strong  anastomosis  with  the  internal  jugular  vein, 
descends  in  company  with  the  vertebral  artery  through  the 
transverse  foramina  canal  of  the  first  six  cervical  vertebrae. 
The  left  vertebral  vein  is  a  tributary  of  the  left  innominate 
(Fig.  78). 

The  innominate  vein  is  formed  by  the  union  of  the  subcla- 
vian  and  the  external  jugular.  Sometimes  the  vertebral  vein 
joins  also  in  the  union  instead  of  emptying  into  the  superior 
vena  cava.  The  subclavian  vein  returns  the  blood  from  the 


THE   VASCULAR    SYSTEM. 


arm,  and  accompanies  the  subclavian  artery. 

jugular    veins    are    large 

vessels    lying    on    either 

side  of  the  neck  beneath 

the      platysma      myoides 

muscle.     When  the  skin  is 

removed,    the    veins    are 

plainly  seen  through  this 

very    thin    muscle.     The 

external  jugular  is  formed 

ventral   to   the   angle   of 

the  mandible  by  the  union 

of  the  internal  and  exter- 

FIG.  78.  VENTRAL  VIEW  OF  THE 
CHIEF  VEINS  OF  THE  TRUNK, 
NECK,  AND  HEAD. 

az,  Azygos;  au,  anterior  auri- 
cular; br,  innominate;  cd, 
caudal ;  cph,  cephalic ;  em, 
anterior  facial;  ex,  ex- 
ternal jugular;  eic,  external 
iliac;  hp,  hepatic;  im,  pos- 
terior facial;  ij,  internal 
jugular;  ims,  inferior  mesen- 
teric ;  ilm,  iliolumbar ;  ilc, 
common  iliac ;  iic,  internal 
iliac ; — ,  inferior  labial;  na, 
anterior  facial;  ov,  ovarian 
or  spermatic;  pan,  posterior 
auricular ;  pd,  pancreato- 
duodenalis;  psy,  superior 
vena  cava;  pst,  inferior  vena 
cava;  prt,  portal;  phrn, 
phrenic;  rn,  renal;  ste, 
superficial  temporal;  st,  gas- 
tro-epiploica  and  coronary;  5»t-4f 
sr,  suprarenal;  sir,  sternal 
or  internal  mammary ;  sp, 
gastrosplenic ;  sm,  superior 
mesenteric;  sbcl,  subclavian; 
tr,  transverse  ;  tg,  submental ; 
vtr,  vertebral;  i,  2,  3,  4,  5, 
6,  the  transverse  foramina  of 
the  first  ^six  cervical  verte- 
brae; w,  intercostals ;  x,  su- 
perior intercostals. 

14 


The  external 


H6  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

nal  maxillary  veins.  The  external  maxillaries  are  united 
by  a  large  transverse  vein.  The  two  tributaries  of  the 
external  jugular  are  the  cephalic  and  the  internal  jugular. 
The  former  is  the  superficial  vein  on  the  lateral  aspect  of 
the  arm,  and  the  latter  is  the  small  vein  returning  blood 
from  the  brain. 

'A  system  of  tube-like  spaces,  called  sinuses,  whose  walls 
are  formed  by  the  dura  mater  lined  with  epithelium,  takes 
the  place  of  the  large  venous  trunks  within  the  cranial 
cavity.  These  sinuses  are  usually  not  filled  by  a  starch  in- 
jection, but  may  be  filled  by  a  gelatin  mass.  They  cannot 
be  dissected  by  the  beginner.  The  superior  longitudinal 
sinus  extends  in  the  median  line  beneath  the  roof  of  the 
skull,  from  the  ethmoid  region  to  the  tentorium  cerebelli, 
where  it  bifurcates  to  form  the  lateral  sinuses,  which  pro- 
ceed laterad  and  ventrad  in  the  substance  of  the  tentorium. 
The  lateral  sinus  emerges  from  the  tentorium  just  caudad 
to  the  petrosal  bone,  where  it  follows  the  groove  to  the 
jugular  foramen.  This  groove  may  be  seen  in  a  bisected 
or  unroofed  skull. 

The  superior  petrosal  sinus  lies  in  the  angle  formed  by 
the  junction  of  the  tentorium  and  the  petrosal  bone,  and 
unites  with  the  lateral  sinus  just  before  it  reaches  the  jugu- 
lar foramen.  The  inferior  petrosal  sinus,  collecting  blood 
from  the  base  of  the  brain,  lies  in  the  groove  ventral  to 
the  petrosal  bone,  and  unites  with  the  lateral  sinus  at  the 
jugular  foramen.  The  union  of  these  sinuses  at  this 
foramen  forms  the  internal  jugular  vein,  which  extends 
deep  beneath  the  muscles  of  the  neck  with  the  carotid 
artery.  It  joins  the  external  jugular  opposite  the  shoulder- 
joint.  At  the  base  of  the  skull  the  internal  jugular  gives 
off  a  large  transverse  anastomosing  vein  to  the  vertebral, 
so  that  the  blood  from  the  vein  may  return  partly  by  the 
latter  vessel. 


THE  VASCULAR   SYSTEM. 


147 


The  pulmonary  veins  convey  the  pure  blood  from  the 
lungs  to  the  left  auricle.  There  are  three  main  trunks  from 
each  lung.  These  six  veins  are  arranged  in  pairs  (Fig.  71), 
constituting  a  left  pair  from  the  left  lung;  a  median  pair, 


.tn 


FIG.  79.  A,  VENTRAL  VIEW  OF  HEART  AND  MAIN  ARTERIES  IN  THE  TRUNK 
OF  THE  RABBIT.  B,  ARTERIES  OF  MAN. 

a,  Right  auricle;  ca,  left  carotid;  c.  ax,  coeliac  axis;  *.  n,  innominate; 
il,  common  iliac;  i.  m,  inferior  mesenteric;  /.  r,  left  renal;  r.  r, 
right  renal ;  r.  c,  right  intercostals ;  sin,  superior  mesenteric ;  spm, 
spermatic;  sa,  sacral;  sb,  left  subclavian. 

composed  of  one  branch  from  the  right  and  one  from  the 
left  lung;  and  a  right  pair  from  the  right  lung.  Each  pair 
forms  a  common  trunk  before  entering  the  auricle.  In 
order  to  demonstrate  these  veins  one  must  remove  the  heart 


M8  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

and  lungs  from  an  injected  cat,  and  carefully  dissect  away 
the  fatty  and  connective  tissues  enveloping  the  vessels. 

The  peripheral  connection  between  the  arteries  and  veins 
is  by  means  of  capillaries,  which  are  microscopic  vessels 
with  an  extremely  thin  wall  composed  of  a  single  layer  of 
epithelial  cells.  These  capillaries  are  so  abundant  every- 
where in  the  flesh  that  a  needle  cannot  be  inserted  without 
penetrating  some.  They  form  a  kind  of  mesh  or  network, 
so  that  every  cell  may  be  supplied  with  oxygen  and  food 
and  discharge  its  waste  matter.  All  the  blood  carried  to 
any  portion  of  the  body  by  the  arteries  is  not  returned  by 
the  veins,  as  a  considerable  amount  of  the  plasma  and  some 
of  the  white  corpuscles  escape  through  the  thin  capillary 
walls  and  are  returned  to  the  circulation  by  a  system  of 
vessels  called  lymphatics  (Fig.  80). 

PRACTICAL   QUESTIONS    AND    SUGGESTIONS. 

1.  What  holds  the  heart  in  place? 

2.  Draw  the  ventral  aspect  of  the  heart  with  the  pericardium  re- 
moved and  label  all  features. 

3.  When  the  heart  is  detached  from  the  body,  how  do  you  distin- 
guish the  dorsal  from  the  ventral  aspect? 

4.  How  many  veins  open  into  each  auricle? 

5.  What  arteries  lead  from  each  ventricle? 

6.  After  dissecting  write  a  detailed  description  of  the  valves  of  the 
heart. 

7.  Describe  the  differences  in  the  appearance  of  the  walls  of  the 
aorta  and  vena  cava. 

8.  From  your  dissection  write  a  description  of  the  features  seen  in 
each  cavity  of  the  heart. 

9.  Name  the  branches  of  the  thoracic  aorta  in  order. 

10.  Name  the  branches  of  the  abdominal  aorta  and  tell  what  organs 
each  supplies. 

11.  Draw  the  cceliac  axis  and  its  branches  throughout  their  course 
and  label  all  parts. 

12.  Show  by  a  drawing  the  relations  of  the  aorta  and  venae  cavse 
throughout. 

13.  Make  a  diagrammatic  cross-section  of  the  neck,  showing  location 
of  arteries  and  veins. 


THE   VASCULAR   SYSTEM.  H9 

14.  Describe  the  three  routes  by  which  blood  may  reach  the  brain 
and  the  two  routes  by  which  it  may  be  returned  to  the  heart. 

15.  Name  the  arteries  arising  from  the  arch  of  the  aorta. 

16.  Draw  the  inner  or  medial  aspect  of  your  dissection  of  the  arteries 
of  the  thoracic  limb  and  label  all  parts. 

17.  Draw  cross-section  of  arm  at  middle  of  humerus  to  show  location 
of  main  artery  and  vein. 

18.  Draw  cross-section  of  the  middle  region  of  the  forearm  to  show 
location  of  chief  arteries. 

19.  Draw  outline  of  the  bones  of  the  manus  and  show  relation  of 
arteries  to  bones  as  seen  from  palmar  aspect. 

20.  Draw  outline  of  femur  and  show  course  of  main  artery  in  relation 
to  the  bone  as  seen  from  medial  aspect. 

21.  Draw  outline  of  bones  of  the  pes  and  show  relations  of  the 
arteries  to  the  bones  as  seen  from  the  plantar  aspect. 

22.  At  what  points  in  its  course  is  the  chief  artery  of  the  pelvic  limb 
most  superficial? 

23.  Describe  the  difference  in  structure  of  a  vein  and  an  artery. 

24.  What  veins  open  into  each  auricle  of  the  heart? 

25.  Name  the  veins  returning  the  blood  from  each  organ  of  the 
abdominal  cavity. 

26.  Draw  the  portal  system  and  label  all  vessels. 

27.  Describe  the  veins  returning  the  blood  from  the  head. 

28.  Describe  the  chief  blood  sinuses  in  the  skull. 

29.  Where  are  the  valves  found  in  the  blood-vessels? 

30.  If  the  brachial  vein  were  cut,  how  could  the  blood  from  the 
manus  reach  the  heart? 

THE  LYMPHATIC  SYSTEM. 

The  lymphatics  constitute  that  part  of  the  vascular  sys- 
tem which  collects  the  colorless  fluid  called  lymph  from 
the  tissues,  and  the  chyle  from  the  small  intestine,  and  con- 
veys them  to  the  external  jugular  veins.  The  portion  of  the 
lymphatic  system  originating  in  the  villi  of  the  small  in- 
testine and  conveying  the  chyle  to  the  left  thoracic  duct  is 
known  as  the  lacteals  (Fig.  65,  b). 

The  lymphatic  system  consists  of  four  parts:  (i)  the 
lymphatic  spaces  between  the  skin  and  muscles  in  all 
parts  of  the  body,  the  spaces  between  the  muscles  adjacent 
to  the  bones,  and  internal  spaces  such  as  those  enclosed  by 


r5°  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

the  peritoneum  and  pleura;  (2)  minute  thin-walled  vessels 
beginning  by  capillary  mouths  in  the  spaces  just  described 
and  leading  to  larger  vessels  which  empty  into  the  tracheal 
trunks  or  thoracic  duct;  (3)  the  glands,  which  vary  in  size 
from  a  mustard-seed  to  two  centimeters  in  diameter,  and 
are  located  chiefly  on  the  side  of  the  neck,  in  the  axillary 
region,  at  the  bifurcation  of  the  trachea;  in  the  inguinal 
region,  lumbar  region,  and  mesentery;  (4)  the  two  tracheal 
trunks  and  thoracic  duct  (Fig.  80). 

One  of  the  largest  of  the  lymphatic  spaces  is  the  greater 
cavity  of  the  peritoneum.  The  cavity  of  the  lesser  perito- 
neum, a  large  lymphatic  space,  may  be  shown  by  separating 
the  layers  of  the  great  omentum  carefully.  The  cavity  of 
the  pleura  within  the  chest  is  also  a  large  lymphatic  space. 
Numerous  small  lymph  spaces  are  present  in  all  parts  of  the 
body.  The  lymphatic  capillaries  originating  in  these  spaces 
are  invisible  to  the  naked  eye,  but  their  union  into  larger 
vessels  may  be  demonstrated  satisfactorily  in  a  cat  just 
killed,  by  pulling  forward  the  tongue,  and  injecting  very 
slowly  beneath  the  skin,  on  its  ventral  aspect  five  or  ten 
centimeters  of  a  two  per  cent,  solution  of  Berlin  blue  in 
warm  water. 

The  lymph  glands  (Fig.  80)  of  the  cat  are  not  nearly  so 
numerous  as  in  man.  The  largest  lymph  gland  is  the 
pancreas  Aselli  in  the  mesentery.  It  is  considerably  flat- 
tened and  about  two  centimeters  long.  A  few  other  very 
small  lymphatic  glands  are  also  present  in  the  mesentery. 
The  two  largest  lymph  glands  of  the  head  are  just  beneath 
the  skin  craniad  of  the  submaxillary  gland.  On  the  side 
of  the  neck  beneath  the  cephalohumeral  muscle  are  three 
large  lymph  glands  at  the  cranial  border  of  the  scapula. 
A  small  axillary  gland  lies  on  the  caudal  side  of  the  axillary 
vein  beneath  the  scapula.  A  single  popliteal  gland  is  in  the 
popliteal  space,  an  inguinal  gland  lies  on  each  side  of  the 


THE  VASCULAR   SYSTEM.  15 l 

penis,  two  or  three  iliac  glands  are  near  the  origin  of  the 
femoral  artery,  and  a  few  small  lumbar  glands  lie  in  the 
lumbar  region  of  the  abdominal  cavity. 

All  parts  of  the  body  have  communication  with  the 
lymphatic  vessels,  which  for  the  most  part  are  so  small  as 
to  be  invisible  unless  injected,  when  they  are  easily  recog- 
nized by  their  beaded  appearance  caused  by  the  numerous 
valves  within  them.  There  are  two  systems  of  vessels  in 
the  head  and  extremities — the  superficial  and  the  deep.  The 
former  accompany  mainly  the  superficial  veins,  and  the  lat- 
ter follow  the  deep  veins.  On  the  outer  aspect  of  the  tho- 
racic limb  just  beneath  the  skin  two  vessels  are  present, 
which  flow  into  the  cervical  glands.  They  carry  the  lymph 
from  the  ball  of  the  foot  and  the  skin  of  the  foot  and 
forearm.  One  or  two  deep  lymph-vessels  are  found  ac- 
companying the  brachial  vein  and  artery,  which  convey  the 
lymph  from  the  bones  and  muscles  of  the  arm  to  the  axil- 
lary gland. 

In  the  pelvic  limb  two  or  three  superficial  vessels  are 
present  transmitting  the  lymph  from  the  foot  to  the  pop- 
liteal gland,  whence  two  vessels  proceed  to  the  deep  lym- 
phatic system.  The  lymph  from  the  bones  and  muscles  of 
the  leg  reaches  the  iliac  glands  through  two  or  three  deep 
vessels  lying  near  the  femoral  vein  and  artery.  The  in- 
guinal glands  receive  most  of  the  lymph  from  the  skin  of 
the  leg. 

The  lymph  from  the  superficial  parts  of  the  head  flows 
largely  into  the  submaxillary  glands,  while  that  from  the 
brain,  tongue,  esophagus,  and  larynx  empties  into  the 
laryngeal  glands. 

The  lymph  of  the  right  forelimb,  right  side  of  the  neck 
and  head,  and  right  side  of  the  thoracic  wall  is  received  by 
the  right  tracheal  trunk.  The  left  tracheal  trunk  receives 
the  lymph  from  the  left  side  of  the  head,  neck  and  thoracic 


152 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


wall,  and  the  left  forelimb.  The  thoracic  duct  receives  the 
lymph  from  the  lungs,  heart,  all  the  abdominal  viscera,  and 
muscles,  and  the  hind-limbs.  With  but  few  exceptions,  all 

the  main  lymphatic  vessels  pass 
through  lymphatic  glands  before 
reaching  one  of  the  three  main 
trunks.  In  fact,  the  vessels  bring- 
ing the  lymph  to  the  glands  may 
be  said  to  terminate  there.  They 
are  called  afferent  lymphatics. 
The  lymph  moves  free  through 
the  tissue  of  the  gland,  and  on 
the  opposite  side  is  taken  up  by 
the  efferent  lymphatics. 

The  right  and  left  tracheal 
trunks  lie  on  their  respective  sides 
of  the  trachea  and  empty  into 
the  external  jugular  vein  just  be- 

FIG.    80.      VENTRAL    ASPECT    OF    CHIEF 
LYMPHATIC  VESSELS  OF  THE  CAT. 

a,  Axillary  gland ;  as,  pancreas  Aselli ; 
an,  superficial  lymphatics  from  the 
head ;  b,  bronchial  glands  receiving 
lymph  from  lungs ;  c,  lymphatic  trunk ; 
cr,  cervical  glands;  cy,  laryngeal 
glands ;  d,  vessel  from  diaphragm ;  ej, 
external  jugular  vein;  in,  inguinal 
glands;  il,  iliac  glands;  ju,  junction  of 
thoracic  duct  with  tracheal  trunk ;  /, 
lumbar  glands ;  li,  large  intestine ;  Iv, 
lymph-vessel  from  liver ;  m,  lacteal 
vessel  and  glands  of  mesentery;  n, 
superficial  lymphatics  from  limb ;  o, 
deep  lymph-vessels  from  limb ;  on, 
lymphatics  from  thoracic  wall ;  ol,  ves- 
sel from  abdominal  wall ;  oc,  vessels 
from  limb ;  rec,  receptaculum  chyli ;  s, 
subclavian  vein;  t,  lymphatics  from 
skin  of  leg ;  tr,  tl,  tracheal  trunks ;  va, 
lymph  trunk  from  pancreas  Aselli  to 
thoracic  duct ;  v,  superior  vena  cava ; 
i  and  2,  submaxillary  lymph  glands. 


THE   VASCULAR    SYSTEM. 


'53 


fore  its  junction  with  the  subclavian.  The  opening  is 
guarded  by  a  valve  which  prevents  the  blood  from  enter- 
ing the  lymphatic  trunk. 

The  thoracic  duct  (Fig.  80)  is  the  largest  vessel  of  the 
lymphatic  system,  but  is  usually  invisible  unless  injected. 
It  extends  from  the  region  of  the  kidneys  on  the  dorsal 


FIG.  81.  PHOTOGRAPH  OF  LYMPHATIC  CAPILLARIES  INJECTED  WITH  BERLIN 
BLUE.  They  lie  immediately  beneath  the  skin  on  the  outer  aspect 
of  the  ear. 

a,  Point  of  injection;  the  black  area  is  Berlin  blue  lying  in  the  connec- 
tive-tissue spaces  from  which  the  capillaries  arise;  n,  injection  es- 
caped from  ruptured  vessel. 

aspect  of  the  body  cavity,  along  the  left  side  of  the  spinal 
column,  to  its  opening  into  the  external  jugular  vein  near 
where  the  latter  joins  the  subclavian  vein.  The  caudal  end 


154  ELEMENTS   OF  MAMMALIAN   ANATOMY. 

of  the  thoracic  duct  is  expanded,  forming  the  receptaculum 
chyli.  Numerous  valves  are  present  in  the  duct,  and  give 
to  it  a  moniliform  or  beaded  appearance.  It  receives  all  the 
lymph  from  the  left  abdominal  wall,  both  pelvic  extremities, 
a  large  part  of  the  thoracic  wall,  and  the  thoracic  and  ab- 
dominal viscera. 

DUCTLESS  GLANDS. 

The  spleen,  thyroid  gland,  thymus  gland,  and  suprarenal 
bodies  are  ductless  glands  whose  functions  are  imperfectly 
known.  The  largest  of  these  is  the  spleen,  which  is  of  a 
deep  red  color  in  a  fresh  specimen,  and  lies  in  the  abdominal 
cavity  on  the  left  side  caudad  to  the  stomach  (Fig.  55). 
It  is  about  five  centimeters  long,  two  centimeters  wide,  and 
less  than  a  centimeter  thick.  It  is  composed  of  lymphoid 
tissue  of  two  forms,  supported  by  connective-tissue  tra- 
beculae  which  are  merely  prolongations  of  the  enveloping 
capsule.  The  two  forms  of  tissue  can  be  seen  by  cutting 
the  organ  transversely.  The  dense  lymphoid  tissue  appears 
as  white  spots  less  than  the  size  of  a  pin-head.  They  are 
the  Malpighian  corpuscles.  The  intervening  looser  lymph- 
oid tissue  forms  the  greater  part  of  the  spleen,  and  is  known 
as  the  splenic  pulp.  The  splenic  artery,  a  branch  of  the 
coeliac  axis,  enters  the  spleen  at  its  hilus  and  divides  into 
capillaries  which  terminate  in  irregular  spaces,  thus  per- 
mitting the  blood  to  flow  freely  through  the  splenic  pulp, 
whence  it  is  taken  up  by  the  capillaries  of  the  splenic  vein 
leading  to  the  portal  vein.  In  embryonic  life  the  spleen 
forms  blood-corpuscles,  but  in  postnatal  life  it  seems  to 
destroy  blood-corpuscles.  An  animal  from  which  the 
spleen  has  been  removed  may  live  many  years  in  good 
health. 

The  thyroid  gland  is  composed  of  two  parts  lying  on 
the  lateral  aspects  of  the  trachea,  just  caudad  to  the  larynx. 


THE  VASCULAR   SYSTEM.  155 

Each  part  is  less  than  two  centimeters  long.  The  two  parts 
are  sometimes  connected  by  a  small  isthmus  extending  ven- 
trally  across  the  trachea,  as  in  man.  An  enlargement  of 
this  gland  in  man  is  called  goiter.  An  animal  can  live 
only  a  short  time  after  the  removal  of  the  thyroid  unless 
it  is  fed  thyroids  or  an  extract  of  thyroid  gland.  The 
function  of  the  gland  is  to  supply  iodin  compounds  to  the 
system. 

The  thymus  gland  is  a  median  structure  varying  in  size 
according  to  age.  In  a  cat  about  one-third  grown  it  is 
very  large,  extending  craniad  from  the  heart  along  the 
ventral  aspect  of  the  trachea  three  or  four  centimeters. 
As  the  cat  grows  older,  it  gradually  dwindles,  and  is  en- 
tirely absent  in  aged  specimens.  Its  function  is  unknown. 
It  persists  throughout  life  in  the  lower  vertebrates. 

The  suprarenal  bodies  are  small,  somewhat  bean-shaped 
organs  lying  craniad  of  the  kidneys.  An  animal  from 
which  they  have  been  removed  can  live  but  a  short  time. 
Their  function  is  not  known.  They  are  sometimes  spoken 
of  as  suprarenal  capsules  or  adrenal  bodies. 

The  above-named  ductless  glands  occur  in  all  mammals 
in  the  same  relative  locations.  The  anatomy  of  the  lym- 
phatic system  is  also  exceedingly  similar  throughout  the 
various  orders  of  mammals.  In  some  animals,  especially 
man,  the  lymphatic  glands  are  more  numerous  than  in 
the  cat.  The  tracheal  trunks  are  also  wanting  in  man  and 
a  right  thoracic  duct  about  two  centimeters  long  is  usually 
present.  A  failure  of  the  lymphatics  to  do  their  work 
results  in  dropsy. 

PRACTICAL   QUESTIONS    AND    SUGGESTIONS. 

1.  Which  of  the  four  parts  of  the  lymphatic  system  are  visible  in 
your  specimen  ? 

2.  Describe  size  and  number  of  lymphatic  glands  in  the  mesentery. 

3.  Describe  the  location  of  lymph  glands  present  in  any  other  portion 
of  your  specimen. 


I56  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

4.  How  do  you  distinguish  a  lymph  gland  from  other  glands? 

5.  What  causes  the  lymph  to  flow  in  one  direction  only? 

6.  What  is  meant  by  afferent  and  efferent  lymphatics? 

7.  Which  kind  of  blood-corpuscles   are   found  within   the  lymph- 
vessels  ? 

8.  From  what  regions  does  the  thoracic  duct  receive  the  lymph  ? 

9.  What  glands  receive  the  lymph  from  the  thoracic  limb? 

10.  What  glands  receive  the  lymph  from  the  pelvic  limb? 

11.  Describe   location   of   spleen,   thyroid   and  thymus   glands,   and 
suprarenal  capsules  by  naming  the  organs  with  which  they  are  in  contact. 

12.  Draw  a  cross-section  of  the  spleen  and  label  all  features  visible. 

13.  Draw  a  cross-section  of  the  suprarenal  body  and  label  parts. 

14.  Tell  what  you  know  of  the  functions  of  the  ductless  glands. 

15.  What  is  a  gland? 


THE  RESPIRATORY  SYSTEM. 

Respiration  is  the  process  whereby  the  tissues  are  sup- 
plied with  oxygen  and  relieved  of  their  carbon  dioxid.  In 
mammals,  the  special  organs  of  respiration  are  the  lungs, 
wherein  the  carbon  dioxid  is  received  from  the  blood,  while 
at  the  same  time  the  oxygen  of  the  air  passes  through  the 
thin-walled  capillaries  to  the  red  blood-corpuscles  capable 
of  conveying  it  to  the  cells  throughout  the  body.  Each 
cell  is  composed  largely  of  carbon,  hydrogen,  oxygen,  and 
nitrogen,  and  any  activity  on  the  part  of  the  cell  is  the 
result  of  the  chemical  union  of  some  of  its  elements, 
whereby  several  waste  products  are  formed,  one  of  which 
is  the  gas,  CO2  (carbon  dioxid).  This  gas  is  a  poison  and 
therefore  must  be  eliminated.  It  passes  through  the  thin 
walls  of  the  capillaries  adjacent  to  every  cell,  and  is  trans- 
ferred through  the  veins  to  the  heart  and  thence  to  the 
lungs.  Here  the  pulmonary  artery  divides  up  into  capil- 
laries ramifying  over  the  air  sacs  (Fig.  84),  thus  per- 
mitting the  carbon  dioxid  to  escape  into  the  air  sacs.  Other 
waste  products  resulting  from  chemical  activity  within  the 
cells  are  carried  away  by  the  kidneys  and  sweat  glands. 

The  respiratory  system  consists  of  the  nasal  passages, 
pharynx,  larynx,  trachea,  and  lungs.  The  air  taken  in  at 
the  anterior  nares  is  warmed  in  passing  over  the  mucous 
membrane  of  the  turbinated  bones,  after  which  it  goes  on 
through  the  posterior  nares  (Fig.  18)  to  the  pharynx,  and 
thence  into  the  larynx. 

The  larynx  is  the  cartilaginous  expansion  of  the  cranial 
end  of  the  trachea,  at  the  base  of  the  tongue.  The  basihyal 
bone  is  attached  to  the  cranial  ventral  margin  of  the  larynx 
and  on  each  side  is  a  thyrohyal  bone  (Fig.  20).  Dorsal 

157 


i58  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

to  the  larynx  is  the  esophagus.  By  removing  carefully 
the  muscles  and  fibrous  tissue  from  the  cartilage  the  larynx 
is  seen  to  be  composed  of  five  pieces :  the  epiglottis,  thyroid 
cartilage,  two  arytenoid  cartilages,  and  the  cricoid  cartilage 
(Fig.  20).  The  epiglottis  is  the  small  triangular  cartilage 
that  closes  the  glottis  when  food  passes  into  the  esophagus 
(Fig.  56).  The  thyroid  cartilage  constitutes  the  largest 
part  of  the  larynx.  In  man  it  forms  the  prominence  known 
as  Adam's  apple.  Dorsally  the  two  halves  of  the  thyroid 
cartilage  are  separated,  each  projecting  craniad  into  a 
process  known  as  a  cornu.  The  arytenoid  cartilages  are 
the  two  small  paired  pieces  caudad  to  the  thyroid,  on  the 
dorsal  side.  The  cricoid  cartilage  forms  a  complete  ring 
at  the  caudal  end  of  the  larynx  (Fig.  20). 

There  are  a  number  of  ligaments  connecting  the  various 
parts  of  the  larynx,  the  most  important  of  which  are  the 


FIG.  82.    DIAGRAMMATIC  TRANSVERSE  SECTION  OF  THE  CHEST. 

ao,  Aorta;  br,  bronchus ;  crd,  spinal  cord;  esoph,  esophagus;  hd,  head  of 
rib ;  pa,  parietal  pleura ;  pc,  cavity  of  the  pleura ;  sp,  spinous  process ; 
st,  sternum ;  ib,  tubercle  of  rib ;  tr,  transverse  process ;  vp,  visceral 
pleura ;  t,  thoracic  duct ;  n,  sympathetic  nerve  cord ;  az,  azygos  vein ; 
ire,  trachea ;  v,  pulmonary  veins. 


THE   RESPIRATORY   SYSTEM. 


159 


FIG.  83.  PHOTOGRAPH  OF  A  LUNG  CORROSION  OF  A  PUMA  IN  MORPHO- 
LOGIC MUSEUM  OF  PRINCETON  UNIVERSITY.  The  specimen  was  pre- 
pared by  Mr.  Sylvester.  The  trachea  with  all  its  ramifications  was 
injected  with  white  paraffin,  and  the  pulmonary  artery  with  red 
paraffin,  after  which  the  lung  substance  was  eaten  away  with  acid. 

tr,  Trachea ;  br,  bronchus ;  b,  bronchial  tube ;  c,  bronchiole.  The  pul- 
monary artery  and  its  branches  are  much  darker  than  the  air  tubes. 


J6o  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

vocal  cords.  These  are  of  two  kinds — true  and  false. 
They  are  best  demonstrated  by  dividing  the  larynx,  sagit- 
tally.  The  superior  or  false  vocal  cords  are  the  two 
superior  thyro-arytenoid  ligaments  passing  from  the  aryte- 
noid  to  the  thyroid  cartilage,  at  the  base  of  the  epiglottis. 
The  cat  is  said  to  use  these  cords  in  purring.  The  in- 
ferior or  true  vocal  cords  are  the  inferior  thyro-arytenoid 
ligaments,  consisting,  as  in  man,  of  a  fold  of  mucous  mem- 
brane on  either  side,  just  caudad  to  the  false  vocal  cords 
(Fig.  56).  The  depression  on  either  side  between  the  true 
and  false  vocal  cords  is  the  ventricle.  By  means  of  the 
muscles  attached  to  the  arytenoid  and  thyroid  cartilages, 
the  tenseness  of  the  vocal  cords  is  regulated,  and  the 
various  pitches  of  voice  produced. 

The  trachea,  or  windpipe,  is  the  tube  leading  from  the 
larynx  to  the  lungs  (Fig.  55).  Its  walls  are  prevented 
from  collapsing  by  the'  presence  of  about  forty-five  carti- 
laginous rings  which  are  incomplete  dorsally.  Before  pass- 
ing into  the  lungs  the  trachea  bifurcates  into  a  right  and  a 
left  bronchus.  The  trachea  and  bronchi  are  lined  by 
ciliated  columnar  epithelium.  The  cilia  project  freely  into 
the  lumen  from  the  columnar  walls,  and  are  always  waving 
in  such  a  manner  as  to  carry  the  secreted  mucus  lodged 
thereon  toward  the  mouth,  thereby  preventing  the  lungs 
from  becoming  clogged  with  foreign  material.  Ciliated 
cells  with  the  cilia  in  action  may  be  easily  demonstrated  by 
scraping  very  lightly  a  little  mucus  from  the  posterior  part 
of  the  roof  of  the  frog's  mouth,  and  mounting  the  same  in 
a  drop  of  saliva  on  a  glass  slip,  which  is  then  to  be  examined 
with  a  microscope  magnifying  about  300  diameters.  The 
diaphragm  of  the  microscope  should  be  arranged  so  as  to 
admit  but  little  light. 

The  lungs  together  with  the  heart  fill  up  the  greater  part 
of  the  thoracic  cavity.     In  a  cat  recently  killed  the  lungs 


THE   RESPIRATORY    SYSTEM. 


161 


vein 


may  be  expanded  by  tying  a  piece  of  glass  tubing  on  the 
trachea  and  blowing  into  it  strongly  for  a  few  seconds^ 
Each  lung  is  completely 
invested  by  a  sac  of  deli- 
cate transparent  serous 
membrane  called  pleura 
(Fig.  82).  Each  sac  is 
reflected  at  the  root  or 
the  lung,  where  the  blood- 
vessels and  bronchus  enter, 
so  as  to  form  a  parietal 
layer  lining  its  half  of  the 
thoracic  cavity.  The  me- 
dian space  between  the 
two  sacs  is  called  the 
mediastinum.  The  ante- 
rior or  ventral  mediasti- 
num contains  blood  vessels 
and  the  thymus  gland. 
The  dorsal  or  posterior 
mediastinum  lodges  the  trachea,  esophagus  and  aorta  and 
the  heart  occupies  the  middle  mediastinum. 

Each  lung  is  divided  by  deep  clefts  into  several  lobes. 
The  left  lung  is  composed  of  two  large  lobes  and  a  small 
one.  The  right  lung  consists  of  four  unequal  lobes.  The 
cranial  end  of  the  lung  is  the  apex  and  the  caudal  end,  rest- 
ing against  the  diaphragm,  is  the  base.  The  bronchi,  as 
they  are  continued  into  the  lungs,  subdivide  into  smaller 
tubes,  whose  later  subdivisions  are  the  bronchioles.  The 
latter,  dividing  like  the  branches  of  a  tree,  finally  terminate 
in  blind  pouches  known  as  infundibula  or  alveoli,  the  walls 
of  which  are  thickly  beset  with  microscopic  sac-like  evagina- 
tions  named  air  sacs  (Figs.  83  and  84).  The  walls  of 
these  air  sacs  are  very  thin,  somewhat  like  the  peritoneum. 
15 


FIG.  84.  DIAGRAM  SHOWING  HOW  THE 
AIR  TUBE  OR  BRONCHIOLE  TERMI- 
NATES IN  INFUNDIBULA. 

in,  infundibulum  with  air  sacs  over 
which  numerous  capillaries  lie. 


162 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


Over  them  course  numerous  thin-walled  capillaries,  so  that 
the  carbon  dioxid  of  the  blood  passes  out  into  the  air  as 
the  oxygen  passes  into  the  blood.  Expiration  is  the  process 


FIG.  85. 


PHOTOGRAPH  OF  HUMAN  HEART  AND  LUNGS  FROM  VENTRAL 

ASPECT. 
a,  aorta;  t,  trachea. 


of  forcing  the  air  out  of  the  lungs  which  have  been  filled 
by  an  inspiration  chiefly  effected  by  depressing  the  dia- 
phragm and  elevating  the  ribs.  The  two  processes  together 
are  spoken  of  as  a  respiration. 

PRACTICAL   QUESTIONS    AND    SUGGESTIONS. 

i.  Of  what  four  elements  are  the  soft  parts  of  the  body  largely 
composed? 


THE  RESPIRATORY   SYSTEM.  163 

2.  What  waste  gas  is  formed  in  every  part  of  the  body  exercised? 

3.  Through  what  three  channels  do  waste  materials  pass  from  the 
blood? 

4.  Describe  the  manner  in  which  the  oxygen  of  the  air  reaches  the 
blood. 

-  5.  Write  a  description  of  the  pharynx. 

6.  Bisect  the  larynx  in  the  sagittal  plane,  make  a  drawing  of  the  cut 
aspect,  and  label  all  features. 

7.  How  many  cartilaginous  rings  in  the  trachea  and  what  is  their 
use? 

8.  Describe  as  much  of  the  pleura  as  can  be  seen  in  your  specimen. 

9.  Do  the  right  and  left  bronchi  have  the  same  number  of  main 
branches  ? 

10.  Wrhy  do  the  air  cells  seldom  become  clogged? 

11.  What  muscles  are  largely  used  in  respiration? 

12.  Describe  the  hyoid  bone  as  seen  from  your  dissection. 

13.  What  part  of  this  bone  can  you  feel  beneath  your  mandible? 

14.  How  does  the  carbon  dioxid  given  off  by  the  cells  in  the  foot 
reach  the  lungs? 

15.  What  causes  the  air  to  enter  the  lungs? 

16.  Inflate  the  lungs  of  a  freshly  killed  animal  by  forcing  air  from 
your  lungs  into  a  glass  tube  tied  into  its  trachea. 

17.  After  retaining  a  full  inspiration  of  air  as  long  as  possible,  expire 
it  through  a  glass  tube  into  the  bottom  of  a  two-liter  bottle  and  insert 
into  the  bottle  a  lighted  splinter. 

18.  Describe  the  pulmonary  circulation 


THE  EXCRETORY  AND  REPRODUCTIVE 
SYSTEM. 

As  explained  in  the  last  section,  a  portion  of  the  waste 
products  produced  by  the  activity  of  the  cells  of  the  body 
is  passed  off  through  the  lungs,  but  some  other  outlet  must 
be  provided  for  the  excretions  that  are  not  in  the  form  of 
gases.  These  liquid  excretions,  containing  various  salts 
and  urea,  pass  off  through  the  kidneys  and  the  glands  of 
the  skin. 

The  latter  are  of  two  kinds,  sudoriparous  or  sweat  glands., 
and  sebaceous  or  oil  glands,  with  ducts  opening  into  the 
hair  follicles  near  the  surface.  The  sweat  glands  lie  deeper 
than  the  sebaceous  glands.  The  former  are  subcutaneous 
and  consist  of  a  more  or  less  coiled  tube  with  a  straight 
duct  opening  on  the  surface.  They  are  most  abundant  on 
the  tip  of  the  nose  and  the  balls  of  the  feet.  The  sebaceous 
glands  are  very  numerous  all  over  the  body.  Both  are  of 
microscopic  size. 

A  still  more  important  part  of  the  excretory  system  is 
the  urinary  system,  consisting  of  the  kidneys,  two  ureters 
leading  from  the  kidneys  to  the  bladder,  the  bladder,  and 
the  urethra. 

The  student  should  note  that  the  kidney  is  not  enveloped 
by  the  peritoneum,  like  the  other  abdominal  organs,  but  lies 
dorsad  to  it  and  is  encased  by  a  fibrous  covering  known  as 
the  capsule.  The  hilus  is  that  portion  of  the  concave  sur- 
face where  the  renal  artery  and  vein  and  ureter  enter.  A 
median  longitudinal  section  of  the  kidney  will  show  that 
the  ureter  within  the  kidney  enlarges,  forming  the  pelvis, 
into  which  projects  the  renal  papilla  (Fig.  87).  This  is 
better  demonstrated  in  a  transverse  section. 

164 


EXCRETORY  AND  REPRODUCTIVE  SYSTEMS.   165 


no- 


The  substance  of  the  kidney  is  composed  of  an  outer 
cortical  layer,  about  a  half  centimeter  thick,  and  an  inner 
medullary  substance  adja- 
cent to  the  pelvis,  and  pro- 
jecting into  the  latter  in  the 
form  of  a  papilla.  In  the 
cortical  substance  are  hun- 
dreds of  Malpighian  bodies, 
each  composed  of  a  ball  of 
capillaries  (Fig.  87)  envel- 
oped by  the  invaginated 
enlarged  extremity  of  a 
tubule  which  carries  away 
the  urine  by  a  tortuous 
course  to  the  papilla  (Fig. 
88).  In  the  Malpighian 
bodies  the  water  and  other 
mineral  substances  of  the 
urine  are  extracted  from 
the  blood  by  means  of  the 
epithelial  cells  forming  the 
inner  wall  of  the  capsule  of 
Bowman.  These  urinary 
products  pass  through  the 
proximal  convoluted  tubule 
and  the  loop  of  Henle  to 
the  distal  convoluted  tubule, 
where  they  are  mingled 
with  the  urea  extracted  from 
the  blood  by  the  columnar 
epithelial  cells  of  the  tubule.  From  this  point  the  excretions 
flow  into  the  collecting  tube  which  empties  into  the  pelvis  at 
the  papilla.  In  a  prepared  microscopic  section  of  the  kid- 
ney, these  Malpighian  bodies  and  uriniferous  tubules  may  be 
seen  with  a  microscope  magnifying  about  200  diameters. 


d 


FIG.  86.  VENTRAL  ASPECT  OF  FE- 
MALE URINO-GENITAL  SYSTEM 
WITH  THE  BLADDER  PULLED  TO 
ONE  SIDE. 

a,  Entrance  of  the  urethra  into  the 
vestibule;  ao,  aorta;  bl,  bladder; 
cl,  clitoris ;  en,  cornu  or  horn  of 
the  uterus ;  ft,  Fallopian  tube,  the 
left  one  is  cut  off;  fm,  fimbri- 
ated  extremity  of  the  Fallopian 
tube ;  kd,  kidney ;  /,  ovarian  liga- 
ment; ov,  ovary;  ra,  renal  ar- 
tery ;  rv,  renal  vein  ;  re,  rectum  ; 
ur,  ureter;  ut,  body  of  the 
uterus ;  uth,  urethra ;  1)0,  vena 
cava;  vg,  vagina;  vs,  vestibule. 


1 66 


ELEMENTS   OF   MAMMALIAN   ANATOMY. 


The  ureter  is  a  small  tube  leading  from  the  pelvis  of 
each  kidney  along  the  dorsal  as- 
pect of  the  abdominal  cavity  to 
the  dorsal  and  caudal  end  of  the 
bladder. 

The  bladder  is  the  sac  for  re- 
taining the  urine.     It  lies  ventrad 


FIG.  87.    MEDIAN  LONGITUDINAL  SECTION 
OF  A  KIDNEY. 

cor,  Cortical  substance;  hi,  hilus ;  med, 
medullary  portion;  p,  papilla;  pi, 
pelvis;  u,  pyramids;  ur,  ureter. 


to  the  rectum,  a  little  to  the  right 
of  the  median  line,  being  held  in 
place  by  the  ligamentum  suspen- 
sorium,  a  fold  of  the  peritoneum 
attached  to  the  mid-ventral  line. 
It  is  also  attached  by  lateral  liga- 
ments. On  its  dorsocaudal  aspect 
near  where  the  ureters  empty,  the 
urethra  originates  and  passes  along 
the  ventral  surface  of  the  vagina 
to  the  vestibule,  within  which  it 
opens  (Fig.  86).  In  the  male  it 


FIG.  88.  DIAGRAM  OF  THE 
STRUCTURE  OF  THE  KID- 
NEY BETWEEN  THE  LlNES 

a  AND  c  IN  FIG.  87. 

ar,  Arteries  leading  to  the 
Malpighian  bodies,  only 
one  capsule  being  shown; 
b,  veins  leading  from  the 
capillary  network  about  a 
convoluted  tubule  as  at 
n ;  ex,  line  marking  the 
boundary  between  the  cor- 
tical and  medullary  por- 
tions of  the  kidney;  cp, 
capsule  of  Bowman  en- 
veloping the  bunch  of 
capillaries;  d,  distal  con- 
voluted tubule ;  hi,  Henle's 
loop ;  n,  capillary  network 
about  the  tubule;  t,  the 
bunch  of  capillaries  or 
Malpighian  tuft;  ur,  por- 
tions of  uriniferous  tubu- 
les emptying  into  the  col- 
lecting tubule  c ;  xc,  prox- 
imal convoluted  tubule. 


passes  directly  from  the  bladder 

along  the  ventral  surface  of  the  rectum  to  the  root  of  the 

penis  at  the  pubic  symphysis,  and  thence  on  through  the 


EXCRETORY  AND  REPRODUCTIVE  SYSTEMS.   167 

corpus  spongiosum  to  the  point  of  the  penis.  The  ureter, 
bladder,  and  urethra  consist  largely  of  muscular  tissue,  the 
lining  being  formed  by  mucous  membrane. 

THE  FEMALE  REPRODUCTIVE  SYSTEM. 

The  female  reproductive  organs  are  the  two  ovaries,  a 
pair  of  Fallopian  tubes,  a  uterus,  and  a  vagina.  To 
demonstrate  these,  the  entire  ventral  abdominal  wall  must 
be  removed  and  the  pubic  symphysis  severed  with  the  bone- 
cutters.  The  ovaries  are  the  small  yellowish  oval  bodies 
about  one  centimeter  long  lying  just  caudad  of  the  kidneys, 
against  the  dorsal  abdominal  wall.  From  the  vicinity  of 
each  extends  a  tube  caudad  to  join  its  fellow  in  the  median 
line  ventrad  to  the  rectum  (Figs.  55  and  86).  The  cranial 
portions  of  these  are  the  Fallopian  tubes,  and  the  larger 
caudal  portions  are  the  cornua  of  the  uterus.  The  junc- 
tion of  the  cornua  in  the  median  line  forms  the  body  of  the 
uterus. 

The  Fallopian  tube  is  smaller  in  diameter  than  the  cornu 
of  the  uterus,  generally  more  or  less  contorted,  and  termi- 
nates by  a  firnbriated  expansion  or  mouth  opening  freely 
into  the  abdominal  cavity. 

The  Fallopian  tubes  and  uterus  are  suspended  by  the 
broad  ligament,  or  ligamentum  latum,  which  is  a  fold  of 
the  peritoneum  attached  to  the  dorsal  abdominal  wall.  The 
round  ligament,  or  ligamentum  rotundum,  also  aids  in 
keeping  the  uterus  in  place.  This  appears  as  a  thickening 
of  the  broad  ligament  when  the  latter  is  looked  through 
toward  the  light.  The  round  ligament  extends  from  about 
the  middle  of  the  horn  or  cornu  of  the  uterus  ventrad  of 
Poupart's  ligament,  and  through  the  muscles  of  the  ab- 
dominal wall  beneath  the  skin  of  the  inguinal  region,  where 
it  gradually  loses  itself.  It  is  exceedingly  delicate  and 
thread-like. 


J68  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

The  vagina  extends  from  the  uterus  to  the  vestibule, 
opening  on  the  surface  ventrad  to  the  anus.  The  small 
papilla  just  caudad  of  the  orifice  of  the  urethra  on  the 
ventral  surface  of  the  vestibule  is  the  clitoris,  the  homo- 
logue  of  a  part  of  the  penis  in  the  male.  The  prominent 
circular  fold  of  mucous  membrane  craniad  of  the  orifice  of 
the  urethra  represents  the  hymen,  which  marks  the  separa- 
tion between  the  vagina  and  vestibule.  This  structure  may 
be  shown  by  making  a  median  longitudinal  section  through 
the  vagina.  Bartholiris  glands  lie  on  the  lateral  aspect  of 
the  vestibule,  into  which  their  ducts  open.  Each  one  is 
about  the  size  of  a  small  pea.  The  vagina,  uterus,  and 
Fallopian  tubes  are  lined  with  mucous  membrane  in  which 
are  many  glands.  The  mucous  lining  is  surrounded  by  a 
muscular  coat  especially  thick  in  the  uterus. 

The  ovaries  are  the  organs  producing  the  female  germ 
cells  or  ova  which  when  fertilized  are  known  as  the  eggs 
(Figs.  55  and  86).  One  lies  caudad  of  the  kidney  on  each 
side  and  is  invested  by  peritoneum,  which  should  be  care- 
fully dissected  away.  A  microscopically  prepared  section 
of  the  adult  ovary  magnified  about  100  diameters  will 
reveal  a  number  of  ova  in  a  more  or  less  mature  state. 
Usually  a  peripheral  ring  of  very  young  ova  is  present, 
more  mature  ones  are  near  the  center,  while  one  or  two 
quite  ripe  ova  are  very  near  the  circumference.  As  the 
ova  develop,  a  follicle  or  sac  known  as  the  Graafian  follicle 
is  formed  about  them.  This  is  lined  with  several  layers 
of  epithelial  cells  forming  the  membrana  granulosa.  At 
one  side  of  the  follicle  the  membrana  granulosa  thickens 
and  envelops  the  ovum,  forming  the  discus  proligerus.  The 
cavity  of  the  follicle  is  filled  with  liquor  folliculi.  When 
the  ovum  becomes  almost  mature,  the  walls  of  the  follicle 
have  grown  peripherad,  so  as  to  cause  a  pin-head  pro- 
tuberance on  the  surface  of  the  ovary  clearly  visible  to  the 


EXCRETORY  AND  REPRODUCTIVE  SYSTEMS.   169 

naked  eye.     In  a   fresh  specimen  this  protuberance  may 
be  picked  open  and  the  ovum  expelled  on  a  slide  for  ex- 


•J/rm 


FIG.  89.    SECTION  OF  OVARY.      X  40. 

sr,  Surface  of  the  ovary;  gr,  Graafian  follicle  with  mature  ovum;  o, 
ovum;  c,  cavity  of  the  follicle;  un,  undeveloped  ova;  strm,  stroma 
or  connective  elements  of  the  ovary;  m,  membrana  granulosa;  d, 
discus  proligerus. 

amination  with  the  microscope.  The  ovum  is  scarcely 
visible  to  the  unaided  eye.  The  human  ovum  is  still 
smaller. 

The  ova  of  all  mammals,  except  the  duck-bill  and  spiny 
ant-eater,  are  very  small.  When  the  ovum  becomes  ma- 
ture, the  protruding  wall  of  the  follicle  bursts,  permitting 
its  contents  to  be  received  by  the  expanded  end  of  the 
Fallopian  tube,  whence  it  passes  to  the  uterus.  If  the  male 
element,  the  spermatozoon,  enters  the  ovum,  the  latter  is 
soon  enveloped  by  a  growth  of  mucous  membrane  and 
retained  in  the  uterus  for  development.  Ripe  ova  occur 
near  the  close  of  the  first  year  of  the  cat's  life  and  new 
ones  probably  continue  to  mature  during  the  next  ten  years. 
The  discharge  of  the  ova  from  the  ovary  is  accompanied  by 
a  constitutional  disturbance,  during  which  an  extra  amount 
of  blood  is  sent  to  the  sexual  organs,  and  the  sexual  appetite 
becomes  very  marked.  In  the  human  species  this  dis- 
turbance occurs  about  every  twenty-eight  days.  Mature 
ova  occur  in  the  human  ovary  between  the  thirteenth  and 
forty-eighth  years. 

16 


I7°  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

The  mammary  glands  of  the  adult  female  cat  reach 
their  full  development  when  it  gives  birth  to  young.  They 
may  be  seen  by  carefully  removing  the  skin  from  the  ven- 
tral aspect  of  the  body,  when  they  will  appear  somewhat 
like  a  thin  layer  of  adipose  tissue  extending  from  near  the 
axilla  to  the  pubic  symphysis.  There  are  four  teats  or 
nipples  on  each  side.  In  some  mammals  the  nipples  are 
less  numerous  and  confined  either  to  the  thoracic  or  inguinal 
region.  In  the  elephant,  Chiroptera,  and  Primates  there 
are  but  two  nipples,  and  they  are  thoracic.  In  most 
Ungulates'  the  nipples  are  inguinal. 

THE  MALE  REPRODUCTIVE  SYSTEM. 

The  organs  of  generation  in  the  male  consist  of  the 
testes,  the  ducts  leading  from  the  testes  to  the  urethra,  the 
prostate  gland,  Cowper's  gland,  and  the  penis. 

The  testes  are  two  in  number,  contained  in  a  pouch  of 
integument  called  the  scrotum,  which  hangs  beneath  the 
anus.  Internally  the  scrotum  is  divided  into  two  chambers. 
By  dissecting  away  the  adipose  tissue  covering  the  spermatic 
cord  in  the  inguinal  region  (Fig.  51)  it  may  be  seen  that 
the  cord  and  the  testes  are  enveloped  by  a  tough  sheath. 
This  is  composed  of  cremasteric  fascia  derived  from  the 
aponeurosis  of  the  external  oblique  muscle,  and  of  the  tunica 
vaginalis. 

During  the  fetal  life  the  testes  lie  in  the  abdominal  cavity, 
and  when  they  descend  into  the  scrotum  about  the  time  of 
birth,  a  double  layer  of  peritoneum  is  pushed  down  before 
them  through  the  inguinal  canal,  forming  a  diverticulum 
whose  blind  end  lies  within  the  scrotum,  while  the  con- 
stricted portion  forms  a  channel  for  the  vas  deferens, 
spermatic  nerve,  and  vessels.  These  three  structures  form 
the  spermatic  cord  (Fig.  51).  The  fascia  propria  (tunica 
vaginalis  communis)  is  inseparably  united  with  the  adjacent 


EXCRETORY  AND  REPRODUCTIVE  SYSTEMS. 


parietal  layer  of  the  peritoneum.  The  visceral  layer  of 
peritoneum  is  quite  delicate 
and  transparent  and  lies 
close  to  the  testis.  Immedi- 
ately surrounding  the  latter 
is  a  dense  capsule,  the  tunica 
albuginea,  sending  septa 
into  the  interior.  Within 
the  tunica  vaginalis  is  the 
tunica  albuginea,  closely  in- 
vesting the  testicle  and  ad- 
jacent to  the  epididymis, 
penetrating  the  substance  of 
the  gland,  forming  a  sep- 
tum known  as  the  medias- 
tinum testis  or  corpus  High- 
morianum  (Fig.  90). 

The  testis  is  about  iy2 
centimeters  long  by  i  centi- 
meter thick.  On  its  dorsal 
surface  lies  the  epididymis, 
an  elongated  body  composed 
of  an  enlarged  extremity, 
the  globus  major,  and  an  at- 
tenuated portion,  the  globus 
minor.  The  main  portion 
of  a  testicle  is  composed  of 
many  minute  coiled  tubules, 
tubuli  seminiferi,  which 
unite  into  a  few  tubules 
near  the  surface  of  the  testis 
beneath  the  globus  major, 
into  which  they  extend. 
These  tubules  are  the  vasa 


FIG.  90.  VENTRAL  ASPECT  OF  THE 
MALE  REPRODUCTIVE  ORGANS. 

cr,  One  of  the  crura  of  the  penis ; 
ep,  epididymis  revealed  by  cut- 
ting and  reflecting  vg,  a  piece  of 
the  tunica  vaginalis  and  albu- 
ginea; et,  external  abdominal 
ring;  if,  internal  abdominal 
ring;  in,  inguinal  canal ;  g,  glans 
penis;  gd,  Cowper's  glands;  pe, 
penis;  pr,  prostate  gland;  re, 
rectum;  t,  testis  from  which  the 
tough  sheath  composed  of  the 
levator  scroti  muscle  and  cre- 
master  fascia  has  been  removed, 
leaving  it  enveloped  by  the 
tunica  vaginalis ;  ts,  testicle  from 
which  a  portion  of  the  tunica 
vaginalis  and  albuginea  has  been 
reflected;  uth,  urethra;  ur,  ure- 
ters; vd,  spermatic  cord;  vdd, 
vas  deferens  within  the  abdomi- 
nal cavity;  vg,  tunica  albuginea 
reflected;  vg-,  tunica  albuginea; 
v,  spermatic  vein. 


172 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


efferentia.  The  epididymis  is  composed  of  a  single  greatly 
convoluted  tubule  of  which  the  vas  defer  ens  is  a  continua- 
tion. The  latter  proceeds  craniad  to  the  external  ab- 
dominal ring,  which  it  enters  to  traverse  the  inguinal  canal 
into  the  abdominal  cavity.  It  then  curves  caudad  and 
enters  the  urethra  on  its  dorsal  aspect  in  the  region  of  the 
prostate  gland. 

The  inguinal  canal  begins  with  the  external  abdominal 
ring,  which  is  an  opening  in  the  tendon  of  the  external 

oblique  muscle,  and  ends  with  the 
internal  abdominal  ring,  which  is  an 
opening  in  the  fascia  of  the  trans- 
versalis  muscle  (Fig.  51).  By  acci- 
dent, a  fold  of  the  small  intestine 
in  man  sometimes  descends  through 
the  inguinal  canal,  which  condition 
is  known  as  hernia  or  rupture. 

The  penis  is  a  cylindrical  pointed 
body  about  three  centimeters  long 
when  in  repose.  It  is  composed  of 
two  kinds  of  tissues  arranged  in  three  bundles.  The  corpus 
spongiosum  is  the  median  ventral  bundle,  extending 
throughout  the  length  of  the  organ,  and  at  the  end  forms 
the  glans  or  head.  The  two  dorsal  lateral  bundles  are  the 
corpora  cavernosa.  They  form  the  greater  part  of  the  penis 
proximad  of  the  glans,  and  by  diverging  somewhat  before 
their  attachment  on  either  side  to  the  pubis  and  ischium 
form  the  crura.  The  penis  is  suspended  from  the  wall  of 
the  abdomen  by  a  fold  of  integument  inserted  at  the  base 
of  the  glans,  and  forming  the  prepuce.  The  latter  is  a 
free  projection  of  skin  covering  the  glans.  In  the  midst 
of  the  penis  is  a  small  bone.  The  penis  is  the  organ  of 
copulation,  and  is  composed  of  a  spongy  mass  of  elastic  and 
muscular  fibers  richly  supplied  with  highly  distensible 
blood-vessels  which  when  filled  render  the  organ  erect. 


FIG.    91.      SPERMATOZOA 
OR  MALE  GERM  CELLS. 
Xsoo. 
h,  Head;  t,  tail. 


EXCRETORY  AND  REPRODUCTIVE  SYSTEMS.   ^73 

The  prostate  gland  surrounds  the  urethra  dorsally  and 
laterally  about  two  or  three  centimeters  from  the  bladder? 
This  gland  secretes  a  milky  fluid  which  is  poured  into  the 
urethra  through  many  ducts,  during  copulation,  and  serves 
as  a  medium  for  the  spermatozoa  (Fig.'  90). 

Cowper's  glands  are  two  in  number,  about  the  size  of  a 
pea,  and  lie  in  the  angles  formed  by  the  urethra  and  the 
crura  of  the  corpora  cavernosa.  These  glands  secrete  a 
viscid  fluid  of  unknown  function.  One  duct  from  each 
gland  opens  into  the  urethra. 

REMARKS  ON  THE  MAMMALIAN  UROGENITAL  SYSTEM. 

The  urogenital  system  is  subject  to  some  variations  in 
the  different  orders  of  Mammalia.  In  the  Ornithodelphia, 
the  mammary 'glands  are  devoid  of  teats  and  the  oviducts 
corresponding  to  the  Fallopian  tubes  and  horns  of  the 
uterus  do  not  unite  in  the  median  line  to  form  the  body  of 
the  uterus,  but  unite  with  the  urethra,  forming  the  uro- 
genital canal.  The  latter  opens  into  an  enlarged  terminal 
portion  of  the  rectum,  called  the  cloaca.  The  ureters  also 
open  directly  into  the  cloaca,  so  that  there  is  but  one  ex- 
ternal opening  for  the  genital  and  excretory  products.  In 
the  above  features  the  Monotremes  resemble  the  Amphibia 
and  reptiles.  All  mammals  are  viviparous  except  the 
Monotremata,  which  are  oviparous,  laying  eggs  as  large 
as  those  of  the  robin.  The  Ornithorhynchus  incubates  its 
eggs  in  an  underground  nest,  while  the  Echidna  carries  her 
single  egg  in  a  temporary  abdominal  pouch. 

The  Marsupialia  bring  forth  their  young  in  a  very  im- 
mature condition.  They  are  then  carried  for  several 
months  in  an  abdominal  integumentary  pouch,  the  mar- 
supiuni,  within  which  are  the  nipples.  In  the  Monotremata, 
Cetacea,  Sirenia,  and  elephant  the  testes  do  not  descend 
into  a  scrotum,  but  are  retained  in  the  primitive  location 


174  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

within  the  abdomen.  In  Primates  and  some  Edentates,  the 
uterus  is  merely  a  pear-shaped  body  without  any  cornua, 
the  Fallopian  tubes  leading  directly  into  the  body  of  the 
uterus. 

In  the  ox,  bears,  seals,  and  cetaceans  the  kidneys  are 
distinctly  lobulated.  Internal  evidence  of  lobulation  is  pre- 
sented in  most  mammals  by  the  renal  papillae.  In  the 
embryo,  the  kidneys  of  all  mammals  are  lobulated. 

PRACTICAL  QUESTIONS   AND  SUGGESTIONS. 

1.  What  other  waste  products  besides  CO2  result  from  the  chemical 
action  in  the  tissues  of  the  body? 

2.  Write  a  description  of  all  parts  of  the  urinary  system  visible  in 
your  dissection. 

3.  Bisect  a  kidney  longitudinally  in  the  horizontal  plane,  draw  the 
cut  surface,  and  label  all  features. 

4.  Explain  the  parts  of  a  uriniferous  tubule. 

5.  Wherein  does  the  male  urinary  system  differ  from  the  female? 

6.  Make  a  drawing  of  the  Fallopian  tubes  and  uterus  and  label  all 
parts. 

7.  Describe  location,  size,  external  appearance,  etc.,  of  the  ovary  as 
seen  in  your  specimen. 

8.  How  are  the  female  reproductive  organs  held  in  place? 

9.  Can  you  distinguish  externally  the  termination  of  the  uterus  and 
the  beginning  of  the  vagina? 

10.  Are  there  any  eggs  protruding  from  the  ovary  or  any  cavities 
from  which  eggs  have  been  recently  discharged? 
n.  Describe  a  Graafian  follicle. 

12.  What  must  be  added  to  the  ovum  to  produce  another  animal? 

13.  Name  the  parts  of  the  male  reproductive  system  present  in  your 
specimen  and  locate  them. 

14.  Describe  the  course  of  the  spermatozoon  from  the  testis  to  the 
exterior. 

15.  Do  all  mammals  nourish  their  young  in  the  same  manner? 

16.  What  mammals  incubate  their  eggs  externally? 


THE  NERVOUS  SYSTEM. 

The  nervous  elements  of  the  cat  form  three  systems, 
known  as  the  central,  peripheral,  and  sympathetic.  The 
central  nervous  system  includes  the  brain  and  spinal  cord. 
The  peripheral  system  includes  the  twelve  pairs  of  nerves 
emanating  from  the  brain  and  the  forty  pairs  of  nerves 
emanating-  from  the  spinal  cord  to  supply  the  extremities 
and  trunk.  The  sympathetic  system  is  composed  of  two 
ganglionated  nerve  cords  extending  throughout  the  trunk 
within  the  body  cavity,  one  on  either  side  of  the  vertebral 
column,  and  their  various  branches  to  all  the  viscera,  blood- 
vessels, etc.,  of  the  body  (Figs.  94 


THE  BRAIN. 

The  central  nervous  system  is  known  as  the  cerebro-spinal 
axis.  It  is  composed  of  the  brain  and  spinal  cord.  The 
brain  lies  within  the  cranial  cavity  and  is  protected  by  three 
membranes  called  the  meninges.  These  may  be  demon- 
strated by  cutting  away  the  roof  of  the  skull  with  the  bone 
forceps.  The  dura  mater  is  the  tough  fibrous  membrane 
lining  the  interior  of  the  skull.  It  dips  down  between  the 
two  halves  of  the  cerebrum,  forming  the  jalx  cerebri.  Be- 
tween the  cerebrum  and  cerebellum  in  the  cat  it  is  ossified, 
thus  forming  the  bony  shelf  or  tentorium  cerebelli  (Fig. 
18).  The  second  membrane  of  the  brain  is  the  arachnoid. 
Between  the  dura  mater  and  the  arachnoid  is  the  subdural 
space,  containing  a  fluid  having  the  nature  of  lymph.  The 
arachnoid  is  a  very  delicate  membrane  which  does  not  dip 
down  into  the  clefts  between  the  folds  of  the  brain,  as  is 
the  case  with  the  pia  mater,  but  passes  across  these  de- 
pressions, where  it  may  be  easily  demonstrated  (Fig.  98). 

H75 


I76  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

The  subarachnoidal  space  lies  between  the  arachnoid  and 
pia  mater.  The  pia  mater  is  the  delicate  vascular  mem- 
brane following  so  closely  the  folds  and  clefts  of  the  brain 
that  it  becomes  apparent  only  when  lifted  carefully  by  the 
forceps. 

In  order  to  study  the  brain  satisfactorily  each  student 
should  have  a  specimen  hardened  according  to  directions 
on  page  10,  and  also  should  be  permitted  to  examine  a 
series  of  sections  cut  transversely  about  a  centimeter  thick. 
The  brain  of  a  calf  or  sheep  serves  the  learner's  purpose 
better  than  that  of  a  cat,  as  the  parts  are  larger,  and  they 
are  also  easier  to  procure.  An  additional  advantage  is  also 
found  in  the  fact  that  there  is  some  difference  between  the 
brains  of  the  cat  and  calf,  and  the  student  must  therefore 
rely  more  on  his  own  observations. 

External  Features. — The  brain  is  composed  of  five 
parts :  the  medulla  oblongata,  or  inyelencephalon;  the  pons 
Varolii  and  cerebellum,  forming  the  metencephalon;  the 
corpora  quadrigemina  and  crura  cerebri,  composing  the 
mesencephalon;  the  diencephalon,  including  the  optic 
thalami  and  other  parts  bounding  the  third  ventricle;  and 
the  telencephalon,  or  cerebral  hemispheres.  The  medulla 
oblongata,  sometimes  called  the  bulb  or  stem  of  the  brain, 
is  the  expansion  of  the  spinal  cord  as  it  passes  through  the 
foramen  magnum.  The  pons  Varolii  is  the  bridge  of 
transverse  fibers  seen  on  the  ventral  aspect  of  the  brain  just 
craniad  of  the  medulla  (Fig.  93).  The  cerebellum  or 
little  brain  lies  on  the  dorsal  side  of  the  medulla  and  is 
partly  covered  by  the  caudal  part  of  the  cerebrum.  The 
mesencephalon  is  not  visible  externally  on  the  dorsal  aspect, 
but  may  be  seen  immediately  craniad  of  the  cerebellum  by 
cutting  away  the  cerebrum  (Fig.  96).  The  diencephalon 
is  visible  externally  only  on  the  ventral  aspect  of  the  uncut 
brain,  where  it  forms  the  floor  of  the  third  ventricle.  It 


THE   NERVOUS    SYSTEM. 


77 


may  be  viewed  as  a  whole  if  the  dorsal  half  of  the  cere- 
brum including  the  corpus  callosum  is  cut  away.  The  telen- 
cephalon  or  end  brain  is  composed  of  the  two  large 
hemispheres  partially  surrounding  the  diencephalon  and 
mesencephalon. 

The  brain  is  composed  of  two  kinds  of  matter,  white  and 
gray.  The  former  is -constructed  for  the  most  part  of 
fibers,  while  the  latter  is  formed  largely  of  cells.  The 
outer  or  cortical  portion  of  the 
cerebrum  and  cerebellum  is  a 
layer  of  gray  matter  less  than 
a  half  centimeter  thick,  and  is 
disposed  in  folds  called  gyri  or 
convolutions  with  intervening 
slit-like  depressions  termed 
sulci,  the  more  important  of 
which  are  called  fissures. 

The  four  different  portions 
of  the  cerebrum  are  known  as 
frontal,  parietal,  occipital,  and 
temporal  lobes,  which  occupy 
the  respective  regions  of  the 
cranial  cavity.  The  frontal  and 
parietal  lobes  are  separated  by 
the  crucial  fissure,  extending 
transversely  between  them. 
The  olfactory  lobe  (usually 
torn  off  in  removing  the  brain 
from  the  skull)  projects  from 
the  cranial  portion  of  the 
frontal  lobe.  The  parietal  lobe 
is  marked  by  three  gyri,  named 
according  to  location  gyrus 
marginalis,  gyrus  suprasylvius, 
and  gyrus  ectosylvius  (Figs.  92  and  93).  The  caudal 


•  Fie.    92.      DORSAL    ASPECT    OF 
THE  BRAIN. 

a,  Gyrus  marginalis;  ac,  white 
matter  of  the  cord;  ad,  gray 
matter  of  the  cord;  b,  gyrus 
suprasylvius ;  c,  gyrus  ecto- 
sylvius ;  cr,  crucial  fissure ; 
ce,  lateral  lobe  of  cerebellum ; 
d,  lateral  sulcus ;  e,  supra- 
sylvian  sulcus  ;  lg,  great  longi- 
tudinal fissure;  md,  medulla 
oblongata;  n,  first  spinal 
nerve;  ol,  olfactory  lobe;  p, 
posterior  pyramids  ;  sp,  spinal 
cord ;  v,  vermis  of  cerebellum. 


I78  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

portions  of  the  gyri  marginalis  and  suprasylvius  constitute 
a  portion  of  the  occipital  lobe.  These  two  gyri  are  sepa- 
rated by  the  lateral  sulcus.  The  suprasylvian  sulcus  ex- 
tends between  the  gyrus  suprasylvius  and  the  gyrus  ecto- 
sylvius.  The  splenial  sulcus  (Fig.  95)  separates  the  gyrus 
marginalis  from  the  gyrus  fornicatus  on  the  medial  aspect 
of  the  parietal  and  occipital  lobes.  There  are  no  definite 
sulci  or  fissures  separating  the  parietal,  occipital,  and  tem- 
poral lobes.  The  postrhinal  fissure,  extending  caudad  from 
the  fissure  of  Sylvius,  divides  the  temporal  lobe  into  two 
portions  on  the  ventral  aspect. 

The  ventral  surface  (Fig.  93)  of  the  brain  also  presents 
important  features  which  should  be  noted  by  the  student 
before  investigating  the  internal  structure.  The  anterior 
pyramids,  two  indistinctly  differentiated  bundles  of  fibers, 
occupy  the  middle  of  the  ventral  region  of  the  medulla,  and 
craniad  of  the  pons  help  form  the  peduncles  of  the  cerebrum. 
Laterad  of  each  pyramid  is  the  olivary  projection.  A  broad 
band  of  transverse  fibers  appearing  just  caudad  of  the  pons 
Varolii  and  laterad  of  the  anterior  pyramids  is  the  corpus 
trapezoideum. 

The  pons  Varolii  is  itself  composed  of  a  band  of  trans- 
verse fibers  which  on  either  side  forms  the  middle  peduncle 
of  the  cerebellum.  The  fibers  originate  either  in  cells  of  the 
medulla  or  those  of  the  cerebellum. 

The  crura  cerebri,  or  peduncles  of  the  cerebrum,  the 
ventral  portions  of  which  are  continued  as  the  anterior 
pyramids  (Fig.  93),  are  seen  just  craniad  of  the  pons. 
Their  fibers  unite  the  cerebrum  to  the  rest  of  the  brain  and 
the  spinal  cord.  In  the  space  between  the  crura  and  the 
optic  chiasm  is  a  prominent  projection,  the  terminal  nodular 
portion  of  which  is  the  pituitary  body  or  hypophysis.  It 
occupies  the  pituitary  fossa  of  the  skull  and  is  usually  torn 
off  in  removing  the  brain.  Caudad  of  the  hypophysis  are 


THE   NERVOUS   SYSTEM. 


179 


rl- 


FIG.  93.    VENTRAL  ASPECT  OF  THE  BRAIN. 

2,  3,  4,  5,  6,  7,  8,  9,  10,  n,  12,  The  cranial  nerves;  a,  ophthalmic  branch 
of  the  trigeminal  nerve ;  an,  anterior  pyramids ;  at,  anterior  horn  of 
gray  matter ;  b,  superior  maxillary  branch  of  the  trigeminal  nerve ; 
na  eleventh  cranial  nerve  with  roots  from  the  spinal _  cord;  c, 
mandibular  branch  of  the  trigeminal  nerve ;  ca,  corpus  albicans ;  cb, 
cerebellum ;  cc,  canalis  centralis  ;  en,  cornea ;  ct,  cut  surface  of  spinal 
cord;  ex,  external  rectus  muscle;  cr,  peduncle  of  the  cerebrum;  g, 
Gasserian  ganglion  of  the  trigeminal  nerve;  hi,  pyriform  lobe;  in, 
opening  into  the  tuber  cinereum  revealed  by  removal  of  the  infundi- 
bulum  and  pituitary  body;  i,  internal  rectus;  io,  inferior  oblique;  ir, 
inferior  rectus  ;  MI  and  n2,  first  and  second  spinal  nerves ;  pi,  olfactory 
lobe;  op,  optic  commissure;  ot,  optic  tract;  p,  posterior  horn  of 
gray  matter ;  pt,  anterior  perforated  space ;  pv,  pons  Varolii ;  r, 
medial  or  inner  root  of  olfactory  nerve;  rt,  lateral  root  of  olfactory 
nerve;  pr,  postrhinal  fissure;  sy,  Sylvian  fissure;  s,  superior  rectus 
muscle ;  tz,  corpus  trapezoideum ;  x,  external  arciform  fibers. 


i  So  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

^Y^' 

two  small  rounded  white  bodies,  the  corpora  albicantia. 
The  tuber  cinereum,  a  slightly  elevated  mass  of  gray  matter 
behind  the  optic  chiasm,  bears  on  its  surface  the  funnel- 
shaped  stalk,  the  infundibulum,  to  which  the  hypophysis  is 
attached.  If  the  two  latter  parts  are  removed,  there  is 
seen  a  small  elongated  aperture  through  the  tuber  cinereum 
into  the  third  ventricle  (Figs.  93  and  95). 

The  optic  commissure,  or  optic  chiasm,  is  the  commissure 
formed  by  the  crossing  of  the  optic  nerves  just  craniad  of 
the  tuber  cinereum.  The  prolongation  of  the  optic  nerves 
dorsad  from  the  optic  commissure  forms  the  optic  tracts, 
partly  covered  by  the  temporal  lobes.  On  either  side  of 
the  median  fissure  just  craniad  of  the  optic  chiasm  is  a 
somewhat  triangular  area  known  as  the  anterior  perforated 
space  because  of  the  numerous  vessels  that  enter  the  brain 
in  this  region.  Laterally  this  space  is  bounded  by  the 
lateral  olfactory  tract  or  lateral  root  of  the  olfactory  -nerve, 
which  presents  the  appearance  of  a  band  of  white  fibers 
extending  from  the  olfactory  lobe  into  the  temporal  lobe. 
The  medial  or  inner  root  of  the  olfactory  nerve  is  seen 
adjacent  to  the  median  ventral  line  craniad  of  the  anterior 
perforated  space.  The  olfactory  lobes  project  from  the 
cranial  ventral  portion  of  the  cerebrum  and  give  origin  to 
the  first  pair  of  cranial  nerves. 

Internal  Structure. — The  canalis  centralis,  a  small  canal 
extending  throughout  the  center  of  the  spinal  cord,  enlarges 
in  the  region  of  the  brain,  forming  four  cavities  or  ven- 
tricles communicating  with  each  other  by  narrow  channels. 
The  brain  is  therefore  to  be  considered  as  a  hollow  struc- 
ture. The  first  and  second  ventricles,  also  known  as  lateral 
ventricles,  occupy  the  cerebral  hemispheres  (Fig.  94).  The 
third  and  fourth  ventricles  lie  in  the  median  line,  and  are 
therefore  well  seen  in  a  sagittal  section  of  the  brain  (Fig. 

95). 


THE   NERVOUS   SYSTEM. 


181 


The  Ventricles  of  the  Brain. — The  fourth  ventricle  is 
visible  on  the  dorsal  aspect  of  the  medulla  oblongata  (Eig.. 
95).  It  is  about  three  centimeters  long  by  one  centimeter 
wide,  and  lies  ventral  to  the  cere- 
bellum. This  ventricle  is  merely  an 
expansion  of  the  canalis  centralis  of 
the  spinal  cord.  Its  roof  is  very  thin 
and  consists  of  two  portions,  one  of 
which,  the  superior  medullary  velum, 
sometimes  called  the  valve  of  Vieus- 
sens,  covers  the  cranial  half  of  the  ven- 
tricle; the  other  portion  is  the  inferior 
medullary  velum,  lying  over  the  caudal 
half.  The  latter  velum  is  composed  of 
a  fold  of  pia  mater  tucked  in  between 
the  cerebellum  and  medulla,  in  addition 
to  a  layer  of  epithelial  cells  on  the  ven- 
tricular aspect  of  the  pia  mater.  Some 
nervous  matter  in  addition  to  the  pia 
mater  and  epithelium  forms  the  supe- 
rior velum.  Two  longitudinal  vascular 
fringes  hanging  from  the  roof  of  the 
ventricle  on  either  side  of  the  mid-line,  form  the  choroid 
ple.rus,  which  is  merely  a  network  of  blood-vessels  carried 
by  a  reflected  portion  of  the  pia  mater. 

Craniad  the  fourth  ventricle  is  continued  as  a  small  canal, 
the  tier,  or  aqueduct  of  Sylvius,  which  lies  ventrad  to  the 
corpora  quadrigemina  and  opens  into  the  third  ventricle 
(Fig.  95).  The  latter  is  a  narrow,  vertical,  cleft-like  space 
between  the  optic  thalami.  The  two  thalami  are  united  by 
the  soft  or  middle  commissure,  better  designated  as  the 
massa  intermedia,  extending  through  the  ventricle.  Unless 
this  ventricle  has  been  injected  with  a  starch  mass  through 
the  infundibulum  before  the  brain  was  hardened,  its  cavity 


FIG.  94.  DIAGRAM  OF 
VENTRICLES  OF  THE 
BRAIN  VIEWED  DOR- 
SALLY. 

ah,  Anterior  horn  of 
the  right  lateral 
ventricle ;  as,  aque- 
duct of  Sylvius;  cc, 
canalis  centralis  of 
the  spinal  cord;  3 
and  4,  third  and 
fourth  ventricles ; 
m,  foramen  of 
Monro;  mi,  middle 
horn  or  cornu  of 
the  ventricle. 


1 82  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

will  not  exceed  a  millimeter  in  width.  The  roof  is  formed 
much  in  the  same  manner  as  that  of  the  fourth  ventricle, 
by  a  reflection  of  the  pia  mater  lined  with  epithelium  (Figs. 
95  and  97).  A  sagittal  section  of  the  brain  placed  in  a 
pan  of  water  will  show  the  fold  of  pia  mater  called  velum 
interpositum  extending  craniad  from  the  pineal  gland. 
Two  folds  of  the  pia  mater  hanging  on  either  side  from 
near  the  median  line  form  the  choroid  plexus  as  in  the 
fourth  ventricle.  The  body  of  the  fornix  lies  dorsad  of 
the  membranous  roof  of  the  ventricle.  In  the  floor  lie  the 
corpora  albicantia,  the  infundibulum,  the  tuber  cinereum, 
and  the  optic  commissure.  Craniad  the  third  ventricle 
communicates  with  the  lateral  ventricles  by  slit-like  aper- 
tures, the  foramina  of  Monro,  passing  laterad  and  ventrad 
of  the  anterior  pillars  of  the  fornix  (Figs.  95  and  96). 

The  lateral  ventricles  are  found  in  the  cerebral  hemi- 
spheres ventrad  to  the  corpus  callosum.  They  are  the 
largest  ventricles  of  the  brain.  In  order  to  view  them  satis- 
factorily, the  entire  dorsal  portion  of  the  brain  down  to  the 
corpus  callosum  must  be  cut  away,  and  a  hole  cut  through 
the  corpus  callosum.  A  number  of  cross-sections  of  the 
cerebral  hemispheres  should  also  be  studied. 

Each  ventricle  is  composed  of  a  body  from  which  pro- 
jects an  anterior  cornu  and  a  middle  or  descending  cornu. 
The  former  extends  into  the  frontal  lobe  and  thence  into 
the  olfactory  lobe,  and  the  latter  descends  into  the  temporal 
lobe.  The  roof  of  the  body  of  the  lateral  ventricle  is 
formed  by  the  corpus  callosum  (Figs.  95,  96  and  97)  and 
the  medial  wall  by  the  septum  lucidum,  a  mass  of  gray 
matter  lying  between  the  fornix  and  the  corpus  callosum. 
A  fringe  of  pia  mater  projects  through  the  foramen  of 
Monro  into  the  lateral  ventricle,  where  it  forms  the 
choroid  plexus.  The  lateral  ventricles  are  lined  with  the 
epithelial  layer  common  to  the  other  ventricles. 


THE   NERVOUS   SYSTEM. 


183 


These  cavities  within  the  central  nervous  system  result 
from  the  manner  in  which  the  brain  and  cord  are  formed. 
In  the  embryonic  life  of  most  vertebrates  the  nervous 
system  appears  as  a  trough  of  matter  extending  dorsally 


;>  ; 


/>* 


FIG.  95.    SAGITTAL  SECTION  OF  THE  BRAIN. 

ac,  Anterior  commissure ;  av,  arbor  vitse ;  c,  habena ;  cc,  canalis  centralis ; 
cb,  cerebellum;  cm,  middle  commissure  or  massa  intermedia;  cr, 
sulcus  crucialis ;  cpq,  corpus  quadrigemina ;  ex,  choroid  plexus  of 
third  ventricle — the  dark  line  dorsad  of  ex  is  the  velum  inter- 
positum ;  /,  sulcus  splenialis ;  fr,  frontal  lobe  of  cerebrum ;  fn,  an- 
terior pillars  of  the  fornix;  in,  infundibulum ;  it,  iter,  or  aqueduct 
of  Sylvius ;  k,  genu  of  corpus  callosum ;  hnx,  lamina  terminalis ; 
m,  splenium ;  mr,  sulcus  marginalis ;  med,  medulla  ;  op,  optic  chiasm ; 
oc,  occipital  lobe ;  ol,  olfactory  lobe ;  pn,  pineal  gland ;  po,  pons 
Varolii;  pc,  posterior  commissure;  pv,  inferior  medullary  velum; 
pw,  superior  medullary  velum  or  valve  of  Vieussens;  3  and  4,  third 
and  fourth  ventricles. 

throughout  the  length  of  the  body.  The  sides  of  this 
trough  grow  dorso-mediad,  thus  forming  a  roof  and  there- 
by converting  the  trough  into  a  canal  which  in  the  spinal 
cord  becomes  the  canalis  centralis,  and  in  the  brain  the 
ventricles.  This  continuous  cavity  of  the  central  nervous 
system  contains  a  fluid  having  the  nature  of  lymph. 

The  Commissures  of  the  Brain. — The  paired  portions 
of  the  brain  are  united  across  the.  median  line  by  bands  of 


'84  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

fibers  known  as  commissures,  two  of  which  are  visible  on 
the  ventral  surface  of  the  brain,  and  the  others  may  be 
seen  in  a  sagittal  section  (Fig.  95). 

The  pons  Varolii  is  the  commissure  on  the  ventral  aspect 
of  the  medulla.  Its  fibers  pass  into  the  cerebellum  on 
either  side,  forming  the  middle  peduncle  or  crus  cerebelli 
ad  pontem.  The  optic  commissure  or  optic  chiasm  is 
formed  by  the  crossing  of  the  optic  nerves,  craniad  of  the 
tuber  cinereum.  Some  of  the  fibers  originating  in  the  cells 
of  the  retina  of  one  eye  pass  by  this  commissure  directly 
to  the  cells  in  the  retina  of  the  other  eye,  while  a  second 
set  passes  from  the  eye  to  the  optic  tract  on  the  opposite 
side  of  the  brain,  and  still  a  third  set,  originating  in  one' 
corpus  quadrigeminum,  passes  by  the  optic  commissure 
direct  to  the  opposite  corpus  quadrigeminum  (Figs.  95, 
104). 

The  corpus  callosum  is  the  largest  commissure  of  the 
brain.  It  joins  the  two  cerebral  hemispheres,  and  forms 
the  roof  of  the  lateral  ventricles.  This  broad  plate  of 
fibers  (Figs.  95,  96,  97,  98),  which  may  be  seen  at  the 
bottom  of  the  great  longitudinal  fissure  by  pressing  the 
hemispheres  slightly  apart,  is  about  one  millimeter  thick  and 
three  centimeters  wide.  Laterally  the  fibers  radiate  in  all 
directions  to  the  gray  matter  of  the  cortex.  The  ventral 
bend  of  the  median  cranial  portion  of  the  callosum  is  the 
genu  or  knee.  The  caudal  border  is  the  splenium. 

The  jornix  lies  ventral  to  the  callosum  (Figs.  95  and  97) 
and  consists  of  a  median  plate  of  fibers,  the  body,  two 
posterior  columns,  and  two  anterior  columns  or  pillars. 
The  median  plate  or  body  of  the  fornix  sends  some  fibers 
into  the  ventral  surface  of  the  callosum.  From  the  cranial 
border  of  the  body  near  the  median  line  the  two  anterior 
columns,  or  pillars,  descend  in  a  curve,  forming  the 
cranial  boundary  of  the.  third  ventricle  as  far  ventrad  as 


THE   NERVOUS   SYSTEM.  M$ 

the  anterior  commissure.  Here  the  two  columns  diverge 
slightly  from  the  median  line,  but  continue  their  descent, 
curving  caudad  to  their  termination  in  the  corpora  albi- 
cantia.  The  posterior  columns,  or  crura,  descend  from  the 
caudal  border  of  the  body,  curving  laterad  into  the  median 
cornu  of  the  lateral  ventricle,  and  gradually  unite  with  the 
cornu  ammonis.  The  cornu  ammonis,  or  hippocampus 
major,  is  a  thickened  projecting  fold  of  the  wall  of  the 


FIG.  96.  DORSAL  ASPECT  OF  THE  BRAIN  WITH  THE  CEREBELLUM  AND 
THE  DORSAL  THIRD  OF  THE  CEREBRUM  REMOVED  AND  MOST  OF  THE 
CORPUS  CALLOSUM  CUT  AWAY  FROM  THE  RIGHT  HALF. 

ac,  Right  anterior  corpus  quadrigeminum ;  c,  commissure  of  the  quadri- 
gemina;  ca,  the  united  superior  and  inferior  peduncles  of  the  cere- 
bellum ;  cr,  the  middle  peduncle  of  the  cerebellum ;  cs,  corpus 
st'riatum;  ct,  edge  of  corpus  callosum  cut  slightly  to  the  left 
of  the  median  line;  cal,  dorsal  surface  of  the  callosum  into  which 
a  hole  has  been  cut;  hp,  hippocampus  major,  or  cornu  ammonis,  in 
the  median  cornu  of  the  lateral  ventricle ;  h,  hippocampus  major 
near  where  it  is  joined  by  the  fibers  of  the  crus  of  the  fornix;  i, 
uncut  portion  of  the  callosum;  md,  medulla  oblongata;  n,  anterior 
columns  or  pillars  of  the  fornix;  o,  gray  cortex  of  the  cerebrum; 
p,  posterior  crus  of  the  fornix;  pn,  pineal  gland,  craniad  to  which 
is  the  heavy  white  line,  the  commissure  of  the  habenae  or  taenise 
thalami;  pp,  funiculus  gracilis;  re,  funiculus  of  Rolando;  /,  funic- 
ulus  cuneatus ;  ts,  posterior  corpora  quadrigemina ;  x,  body  of 
the  fornix. 


1 86  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

median  cornu  of  the  lateral  ventricle  (Fig.  96).  The  free 
lateral  margin  of  the  posterior  pillar  or  crus  of  the  fornix  is 
the  ftmbria,  or  tcenia  hippocampi.  Adjacent  to  the  median 
line  in  either  hemisphere,  a  thick  lamina  of  matter,  the  septum 
lucidum,  stretches  from  the  cranial  part  of  the  fornix  dorsad 
to  the  callosum.  The  very  narrow  cavity  formed  by  the  ad- 
herence of  the  margins  of  the  septum  of  one  hemisphere  to 
those  of  the  septum  in  the  other  hemisphere  is  sometimes 
called  the  fifth  ventricle.  Between  each  anterior  pillar  of 
the  fornix  and  the  optic  thalamus  is  a  cleft,  the  -foramen 
of  Monro,  leading  from  the  third  ventricle,  laterad  of  the 
septum  lucidum,  into  the  lateral  ventricle. 

The  three  remaining  commissures  are  known  according 
to  their  location  as  the  anterior,  middle,  and  posterior. 
The  anterior  commissure  (Figs.  95  and  98)  perforates  the 
corpora  striata,  extending  across  the  median  line  imme- 
diately craniad  of  the  anterior  pillars  of  the  fornix.  It  is 
about  two  millimeters  in  diameter.  The  middle  commis- 
sure, or  massa  intermedia,  lies  between  the  optic  thalami. 
It  is  sometimes  called  the  soft  or  gray  commissure.  It  is 
nearly  one  centimeter  in  diameter  and  passes  through  the 
third  ventricle  (Fig.  95).  The  posterior  commissure  is  a 
cord  of  fibers  about  a  millimeter  in  diameter  connecting  the 
caudal  portions  of  the  optic  thalami. 

The  Basal  Ganglia. — A  semi-independent  group  of 
nerve  cells  forming  a  definite  mass  is  known  as  a  ganglion. 
In  the  ventral  portion  of  the  brain  lie  three  pairs  of  large 
ganglia,  called  corpora  quadrigemina,  optic  thalami,  and 
corpora  striata.  To  study  them,  the  entire  dorsal  surface 
of  the  brain  down  to  and  including  the  corpus  callosum 
should  be  removed. 

The  corpora  quadrigemina  (Fig.  96)  forming  the  dorsal 
part  of  the  mesencephalon  lie  craniad  of  the  medulla,  and 
consist  of  an  anterior  pair  and  a  posterior  pair.  The  for- 
mer are  known  as  the  superior  colliculi  and  the  latter  as 


THE   NERVOUS   SYSTEM. 


187 


inferior  colliculi.  The  anterior  pair  lie  nearer  to  the  midline 
than  the  posterior  pair,  which  are  slightly  separated  by  a  de- 
pression occupied  by  the  middle  portion  of  the  central  lobe 
of  the  cerebellum.  The  posterior  pair  are  united  by  a  white 
commissure.  The  posterior  commissure  of  the  brain  unites 
the  cranial  portions  of  the  anterior  pair  (Fig.  95).  Its 
cut  end  may  be  seen  ventrad  to  the  base  of  the  pineal  gland. 


FIG.  97.    CROSS-SECTION  OF  THE  BRAIN  IN  THE  PLANE  x  IN  FIG.  95. 
The  plane  is  just  caudad  of  the  optic  chiasm. 

i  and  2,  First  and  second  or  lateral  ventricles ;  cr,  corpus  callosum ;  cm, 
anterior  pillars  of  f  ornix ;  ex,  choroid  plexus  of  lateral  ventricle  ;  ex', 
choroid  plexus  of  third  ventricle;  cxt,  gray  cortex;  ea,  ependyma 
lining  the  ventricles;  f,  median  longitudinal  fissure;  h,  tsenia 
thalami ;  wr,, middle  commissure,  or  massa  intermedia;  n,  fibers 
of  the  optic  tract  as  they  enter  the  lateral  geniculate  body  s; 
o,  f  ornix ;  r,  caudal  portion  of  nucleus  lenticularis ;  op,  optic 
thalamus ;  oc,  optic  tract  as  it  leaves  the  chiasm ;  si,  septum  lucidum ; 
vn,  part  of  third  ventricle  dorsad  to  the  commissure;  v,  third 
ventricle;  t.  fibers  of  optic  tract. 

Laterally  each  pair  of  the  corpora  quadrigemina  is  pro- 
longed into  two  white  bands,  the  anterior  and  posterior 
brachia.  The  latter  are  about  a  half  centimeter  long,  and 
pass  forward  beneath  a  pisiform  ganglion,  the  corpus  geni- 
culatum  internum  or  mediale.  The  anterior  brachia  pass 
from  the  cranial  end  of  the  posterior  pair  laterad  beneath 
the  caudal  projections  of  the  optic  thalami,  where  they  join 
the  optic  tracts. 


1 88  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

Homologues  of  the  corpora  quadrigemina  exist  in  all 
vertebrates.  In  these  bodies  originate  partly  the  optic 
nerves,  and  therefore  their  size  is  in  proportion  to  the  ani- 
mal's power  of  sight.  In  the  mole,  which  has  little  use  for 
eyes,  the  anterior  pair  is  rudimentary. 

The  optic  thalami  forming  the  sides  of  the  diencephalon 
or  tween  brain  are  the  largest  pair  of  basal  ganglia,  and 
lie  craniad  of  the  corpora  quadrigemina  and  form  the 
lateral  walls  of  the  third  ventricle,  across  which  they  meet, 
forming  the  massa  intermedia,  or  middle  commissure. 

On  the  dorsal  aspect  of  each  thalamus,  near  the  median 
line,  is  a  longitudinal  band  of  white  fibers  called  the  tcciria 
thalami,  which  at  its  caudal  limit  is  united  to  its  fellow  by 
the  commissura  habenae.  The  thalamus  is  composed  largely 
of  gray  matter,  but  there  are  two  important  bundles  of 
fibers,  known  as  the  optic  tract  and  internal  capsule  (Fig. 
97),  appearing  on  its  lateral  surface.  The  optic  tract,  of 
which  the  optic  nerve  is  a  continuation,  arises  by  two  roots, 
the  larger  of  which  comes  from  the  cells  forming  the 
lateral  geniculate  body,  which  is  the  lateral  and  caudal  pro- 
jection of  the  thalamus.  The  internal  capsule,  well  shown 
in  a  transverse  section,  is  composed  of  the  fibers  forming  a 
communication  between  the  cells  of  the  cortex  and  those  in 
the  lower  brain  centres  and  spinal  cord. 

The  pineal  gland,  or  pineal  body  (Fig.  95),  is  a  conical 
projection  about  a  half  centimeter  long,  from  the  caudal 
part  of  the  dorsal  surface  of  the  thalamus.  It  is  a  vestigial 
structure  which  in  some  of  the  lower  vertebrates  in  early 
geological  time  functioned  as  a  third  eye.  In  Hatteria, 
a  New  Zealand  lizard  about  a  foot  long,  the  eye  is  present, 
projecting  slightly  through  a  foramen  in  the  parietal  bone. 
Traces  of  this  third  eye  with  a  lens  have  also  been  noticed 
in  the  embryo  of  the  viper  and  some  of  the  lizards. 

The  corpora  striata  lie  deep  in  the  telencephalon.     They 


THE   NERVOUS    SYSTEM. 


189 


are  the  most  anterior  of  the  basal  ganglia  and  are  somewhat 
pear-shaped,  the  larger  ends  being  craniad  and  nearer  the 
median  line  than  the  caudal  portions,  which  curve  laterad 
around  the  optic  thalami  (Fig.  96).  They  form  a  part  of 
the  floor  of  the  lateral  ventricles,  and  are  pierced  by  the 
anterior  commissure  (Fig.  98),  a  small  cord  of  white  fibers. 
The  corpus  striatum  consists  of  both  white  and  gray 
matter.  The  latter,  composed  of  cells,  is  disposed  in  two 
chief  nuclei  or  masses,  known  as  the  nucleus  caudatus, 
lying  anterior  and  nearer  the  median  line  than  the  nucleus 
lenticularis,  which  is  more  lateral  and  caudal  (Fig.  98). 


an 


FIG.  98.     CROSS-SECTION  OF  THE  BRAIN  THROUGH  THE  ANTERIOR  COM- 
MISSURE. 

an,  Arachnoid;  ce,  external  capsule;  cl,  corpus  callosum;  cm,  anterior 
commissure;  jxc,  falx  cerebri;  /,  great  longitudinal  fissure;  fx, 
anterior  pillars  of  the  fornix;  ic,  internal  capsule;  n,  radiating 
fibers  of  callosum;  in,  septum  lucidum;  nc,  nucleus  caudatus  of 
corpus  striatum ;  I,  nucleus  lenticularis ;  p,  pia  mater ;  vis,  superior 
longitudinal  sinus ;  vn,  third  ventricle ;  v,  lateral  ventricle. 

The  center  of  the  nucleus  lenticularis  is  laterad  of  the  optic 
thalamus  and  dorsad  of  the  crus  cerebri.  A  thin  layer  of 
white  matter,  the  lamina  semicircularis,  separates  the  optic 
thalamus  from  the  nucleus  caudatus.  A  few  fibers  from 
the  cerebral  peduncles  form  the  lamina  semicircularis,  whose 
edge  may  be  seen  in  the  floor  of  the  lateral  ventricle  on  the 
lateral  boundary  of  the  nucleus  caudatus.  A  group  of 


19°  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

fibers,  known  as  the  internal  capsule,  separates  the  optic 
thalamus  from  the  nucleus  lenticularis,  laterad  of  which 
is  the  external  capsule,  a  group  of  fibers  probably  descend- 
ing from  the  cells  of  the  cerebral  cortex.  The  two  nuclei 
of  the  corpus  striatum  are  connected  by  fibers,  and  other 
fibers  connect  these  nuclei  with  the  cortex  of  the  cerebrum 
and  the  optic  thalamus. 

The  Medulla  Oblongata. — The  medulla  oblongata,  or 
myelencephalon,  is  the  stem  of  the  true  brain  and  extends 
from  the  point  of  origin  of  the  first  spinal  nerve  to  the 
pons  Varolii.  The  cerebellum  must  be  removed  in  order 
to  study  carefully  the  features  of  the  medulla,  and  as  it  is 
cut  away  the  student  should  notice  just  ventrad  to  it  the 
very  thin  roof  of  the  fourth  ventricle.  Its  caudal  portion, 
composed  of  a  reflection  of  the  pia  mater  lined  with  epi- 
thelium, takes  the  name  of  inferior  medullary  velum,  and 
the  cranial  part,  formed  of  pia  and  a  thin  layer  of  nervous 
matter,  is  called  the  anterior  medullary  velum  ( Fig.  95 ) . 

The  fourth  ventricle  (Figs.  95  and  96)  is  an  enlargement 
of  the  canalis  centralis  of  the  cord.  Two  bands  of  fibers 
called  clave? ,  the  three  peduncles  or  crura  of  the  cerebellum, 
and  the  posterior  corpora  quadrigemina  form  its  lateral 
boundaries.  Its  cavity  is  shallow  and  pointed  at  either 
extremity.  The  floor,  called  fossa  rhomb oidea,  is  formed 
by  the  continuation  of  the  gray  matter  of  the  spinal  cord. 
Where  the  ventricle  is  widest  a  tract  of  fibers,  the  stria 
medullaris,  arises  from  the  midline  and  proceeds  laterad 
to  help  form  the  auditory  nerve. 

Laterad  of  the  clava  a  larger  band  of  fibers,  the  funiculus 
cuneatus,  runs  parallel  with  a  more  lateral  lying  bundle,  the 
funiculus  cuneatus  lateralis,  or  funiculus  of  Rolando.  The 
band  of  fibers  on  either  side  uniting  the  cerebellum  to  the 
medulla  oblongata  is  the  restiform  body,  or  inferior  peduncle 
of  the  cerebellum.  On  the  ventral  aspect  of  the  medulla 


THE  NERVOUS  SYSTEM.  I91 

may  be  seen  the  anterior  pyramids,  composed  of  a  band  of 
fibers  lying  on  either  side  of  the  median  line  and  apparently 
emerging  from  the  pons.  They  form  a  section  of  the 
crossed  pyramidal  or  motor  tract  connecting  the  brain  with 
the  cord.  The  olivary  eminence  lies  just  laterad  of  the 
pyramid.  The  fact  that  seven  posterior  cranial  nerves 
originate  from  the  medulla  shows  the  importance  of  this 
part  of  the  brain.  The  destruction  of  the  respiratory 
centers,  or  vital  knot,  lying  ventrad  to  the  caudal  end  of  the 
fourth  ventricle  causes  instant  death. 

The  Cerebellum,  or  Little  Brain. — The  cerebellum, 
which  in  the  cat  lies  caudad  of  the  cerebrum  and  dorsad 
of  the  medulla,  resembles  the  cerebrum  in  being  composed 
of  an  outer  layer  of  gray  matter  or  cells  and  an  inner 
mass  of  white  matter  made  up  of  fibers.  While  within  the 
cerebrum  there  are  several  important  ganglia  or  masses  of 
gray  matter,  in  the  cerebellum  only  one  chief  mass  of  gray 
matter,  the  corpus  dentatum,  is  present  in  each  hemisphere. 

The  outer  layer  of  gray  matter,  known  as  the  cortex,  is 
folded  into  numerous  convolutions,  between  which  are  deep 
sulci  (Fig.  95).  The  central  core  of  white  matter  forms 
an  arborescence  known  as  the  arbor  vitcu. 

The  cerebellum  (Fig.  92)  is  seen  to  consist  externally 
of  two  lateral  portions,  the  cerebellar  hemispheres,  a  median 
vermiform  process  and  three  pairs  of  peduncles  or  crura 
which  are  bands  of  fibers  uniting  it  with  other  parts  of  the 
brain  and  cord  (Fig.  96).  The  separation  between  the 
hemispheres  and  vermis  or  vermiform  process  is  most 
marked  on  the  cranial  aspect. 

The  peduncles  are  named,  according  to  their  location, 
superior,  middle,  and  inferior.  The  middle  peduncle,  or 
brachium  pontis,  is  a  dorsal  prolongation  of  the  fibers  of 
the  pons  Varolii  (Fig.  93).  In  order  to  display  the  other 
peduncles  a  portion  of  the  cerebellum  must  be  cut  or  picked 


I92  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

away  with  the  forceps.  The  superior  one,  known  also  as 
the  brachium  conjunctvvum,  extends  as  a  cord  of  fibers 
along  the  cranial  half  of  the  fourth  ventricle  and  then 
beneath  the  corpus  quadrigeminum.  The  inferior  pedun- 
cle, or  restiform  body,  forms  part  of  the  boundary  of  the 
caudal  half  of  the  fourth  ventricle  and  enters  the  cere- 
bellum between  the  other  two  peduncles.  It  is  composed 
of  fibers  from  the  spinal  cord  and  medulla. 

PRACTICAL  QUESTIONS  AND  SUGGESTIONS. 

1.  Describe  the  meninges  of  the  central  nervous  system. 

2.  Which  of  the  five  parts  of  the  brain  are  exposed  dorsally? 

3.  Draw  the  lateral  aspect  of  the  brain  and  label  all  features. 

4.  Draw  the  ventral  aspect  of  the  brain  and  label  all  features. 

5.  Draw  the  dorsal  aspect  of  the  brain  after  the  dorsal  portion,  in- 
cluding corpus  callosum  and  fornix,  has  been  removed. 

6.  Describe  the  differences  existing  between  the  gyri  and  sulci  of 
your  specimen  and  the  one  described  in  the  text. 

7.  Write   a   description   of   the   ventricles,   giving   dimensions   and 
boundaries. 

8.  Describe  the  attachment  of  the  pineal  body. 

9.  Which  of  the  cranial  nerves  derive  their  name  from  their  func- 
tion? 

10.  Name   the   foramina   giving   passage   to    one    or   more    of    the 
cranial  nerves. 

11.  From  which  of  the  five  parts  of  the  brain  do  most  of  the  cranial 
nerves  originate? 

12.  Describe  the  choroid  plexus. 

13.  What  is  the  internal  capsule? 

14.  Draw  a  cross-section  of  the  brain  made  by  cutting  through  the 
optic  commissure  and  label  all  parts. 

15.  Draw  a  cross-section  of  the  brain  made  by  cutting  through  the 
middle  commissure  and  label  all  parts. 

16.  Draw  a  cross-section  of  the  brain  made  by  cutting  through  the 
corpora  quadrigemina  and  label  all  parts. 

17.  Write  a  description  of  the  corpus  callosum. 

18.  Which  is  the  smallest  commissure  of  the  brain? 

19.  Explain  the  difference  in  structure  between  the  white  and  gray 
matter. 

20.  Describe  the  cerebellum. 


THE   NERVOUS    SYSTEM. 


'93 


THE  SPINAL  CORD. 

The  spinal  cord  extends  from  the  foramen  magnum 
through  the  vertebral  canal.  It  is  more  or  less  cylindrical 
throughout  and  has  a  diameter  of  about  one  centimeter 
except  in  the  lumbosacral  region,  where  it  grows  gradu- 
ally smaller  until  it  is  only  one  or  two  millimeters  in 
diameter.  In  order  to  study  the  cord,  one  should  have  a 


n 


FIG.  99.    PHOTOMICROGRAPH  OF  CROSS  SECTION  OF  HUMAN  SPINAL  CORD. 

a,  Arachnoid  membrane ;  an,  ventral  side  in  which  appears  the  deep 
anterior  fissure ;  d,  dura  mater ;  n,  one  of  several  nerve  bundles ; 
the  tiny  white  spot  in  the  center  of  the  dark  gray  matter  is  the 
canalis  centralis;  p,  pia  mater.  X  5. 

mounted  transverse  microscopic  section,  and  an  entire  cord 
in  situ  with  the  dorsal  wall  of  the  vertebral  canal  removed, 
so  that  the  exit  of  the  spinal  nerves  may  be  seen. 

The  membranes  (Fig.  99)  which  envelop  the  spinal  cord 
18 


194  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

are  the  same  as  those  that  envelop  the  brain.  The  dura 
mater  is  the  external  tough  coat;  the  pia  mater,  the  internal 
delicate  vascular  coat  sending  a  process  deep  into  the  ante- 
rior fissure  on  the  ventral  side;  and  the  arachnoid,  the  very 
thin  membrane  between  the  two  preceding.  The  arachnoid 
lies  close  against  the  dura  mater,  but  is  separated  from  the 
pia  mater  by  the  subarachnoid  space,  which  is  filled  with  a 
serous  fluid  called  the  cerebrospinal  fluid.  It  is  apparently 
the  same  as  that  in  the  ventricles  of  the  brain,  and  seems  to 
be  of  a  lymphoid  nature.  In  fact,  the  subarachnoidean 
space  is  merely  a  large  lymph  space  similar  to  the  cavities  of 
the  pleura  and  peritoneum.  This  lymph,  or  cerebrospinal 
fluid,  probably  escapes  from  the  thin  walls  of  the  capillaries 
covering  the  pia  mater  and  is  taken  up  by  lymphatic  vessels 
which  begin  in  open  mouths  on  the  walls  of  the  space. 

The  cord  presents  two  enlargements,  the  cervical,  whence 
issue  the  nerves  of  the  forelimbs,  and  the  lumbar,  giving 
origin  to  the  nerves  of  the  posterior  limbs.  p  Two  deep 
fissures,  the  anterior  median  and  the  posterior  median. 
penetrate  about  one-third  through  the  cord,  incompletely 
dividing  it  into  halves  longitudinally.  The  pia  mater  is 
prolonged  into  the  anterior  fissure,  but  not  into  the  pos- 
terior fissure.  Slightly  laterad  of  the  anterior  median 
fissure  issue  the  anterior  roots  of  the  spinal  nerves,  and  at 
about  the  same  distance  from  the  posterior  median  fissure 
are  the  posterior  roots  of  the  spinal  nerves.  These  two 
roots  unite  about  one  centimeter  from  their  origin  (Fig. 
93).  On  the  posterior  or  sensory  root  is  a  small  ganglion 
located  very  near  the  junction  of  the  two  roots.  The. 
common  spinal  nerve,  formed  by  the  union  of  the  two  roots, 
almost  immediately  divides  into  four  branches,  one  of 
which,  the  dorsal,  supplies  the  muscles  and  skin  along  the 
vertebral  column;  a  second,  the  ventral  branch,  supplies  the 
limbs  or  intercostal  spaces;  while  the  other  two  branches, 


THE   NERVOUS   SYSTEM. 


195 


rami  communicant es,  join  the  adjacent  ganglion  of  the 
sympathetic  cord  (Fig.  107).  Each  of  the  four  branches 
contains  both  motor  and  sensory  fibers,  or,  in  other  words, 
fibers  from  both  roots. 

The  exit  and  entrance  of  the  nerve  roots  divide  the  white 
matter  of  the  lateral  half  into  three  columns  named,  accord- 
ing to  their  location,  the  anterior  column,  the  lateral  column, 
and  the  posterior  column.  The  first  is  ventral  to  the  an- 
terior nerve  roots,  the  last  is  dorsal  to  the  posterior  nerve 
roots,  while  the  lateral  column  is  between  the  roots. 

The  elements  of  the  spinal  cord,  like  those  of  the  brain, 
are  of  two  kinds — the  cells  composing  the  gray  matter  and 


FIG.  100.  DIAGRAMMATIC  CROSS-SECTION  OF  THE  SPINAL  CORD.  The  cells 
and  fibers  are  represented  too  few  and  too  large  in  proportion  to  the 
size  of  the  cord. 

ag,  Anterior  horn  or  column  of  gray  matter ;  a,  nerve  process  of  the  cell 
c ;  an,  anterior  root ;  cc,  canalis  centralis ;  c,  one  of  many  cells  form- 
ing the  ganglion  on  the  posterior  root;  d,  posterior  fissure;  e,  cell 
giving  off  an  axone  into  the  anterior  root;  dn,  dorsal  branch; 
f,  cut-off  fibers;  gn,  ganglion  of  posterior  root;  i,  axone  of  the 
cell  io  ;  nc,  junction  of  anterior  and  posterior  roots ;  ps,  posterior 
root  of  nerve ;  pg,  posterior  horn  of  gray  matter ;  s,  terminal  arbor- 
ization of  part  of  fiber  from  c ;  v,  anterior  median  fissure ;  vn,  ven- 
tral branch  of  nerve ;  van,  axone  of  anterior  horn  cells ;  x,  the  part 
of  the  posterior  root  fiber  extending  caudad  in  the  cord. 

the  fibers  composing  the  white  matter.  While  in  the  brain 
the  gray  matter  is  largely  on  the  surface,  forming  the 
cortex,  in  the  cord  it  occupies  the  central  region.  A  canal, 


196 


ELEMENTS   OF   MAMMALIAN   ANATOMY. 


the  canalis  centralis,  about  one-half  a  millimeter  in  diameter, 
extends  throughout  the  cord,  opening  into  the  fourth  ven- 
tricle of  the  brain.  A  cross-section  of  the  cord  shows  the 
gray  matter  arranged  in  the  shape  of  a  letter  H.  The 
ventral  columns  of  gray  matter  are  the  anterior  horns,  and 
the  posterior  columns,  the  posterior  horns  (Fig.  100). 

Many  of  the  fibers  extend  in  a  longitudinal  direction 
throughout  the  cord,  but  the  roots  of  the  spinal  nerves  upon 
entering  the  cord  run  transversely  a  longer  or  shorter  dis- 


FIG.  101.    CELL  FROM  THE  CENTRAL  NERVOUS  SYSTEM.     X  100. 

a,  Dendrites  or  protoplasmic  processes ;  ax,  axone ;  n,  nucleus  of  the 

cell  body. 

tance,  and  in  many  cases  cross  to  the  opposite  side.  Num- 
erous experiments  show  that  the  anterior  root  fibers  are,  for 
the  most  part,  the  axones  of  the  cells  in  the  anterior  horn 
(Fig.  102). 


THE   NERVOUS    SYSTEM. 


197 


FIG.  102.    DIAGRAM    SHOWING  THE  RELATION  OF  SOME  OF  THE  CELLS  AND 
FIBERS  OF  THE  SPINAL  CORD.     Lateral  aspect  of  the  cord. 

a,  Anterior  median  fissure ;  ac,  cells  of  the  anterior  horn ;  an,  anterior 
root  of  spinal  nerve ;  c,  axone ;  co,  collateral  fibers ;  e,  fibers  con- 
necting higher  brain  centers  with  cerebellum;  fi,  sensory  fibers  of 
fillet  to  the  brain ;  g,  gn,  go,  ganglion  of  posterior  root ;  gr,.  gray 
matter ;  ir,  fibers  of  the  posterior  sensory  tract ;  I,  fibers  to  cere- 
bellum; m,  cell  in  the  anterior  horn  or  column  of  gray  matter; 
n,  spinal  nerves ;  o,  cells  in  the  posterior  horn  or  column  of  gray 
matter ;  nc,  nucleus  gracilis  and  nucleus  cuneatus ;  nr,  nucleus  ruber ; 
r,  a  fiber  of  posterior  root ;  rb,  ganglion  cells  of  medulla ;  s,  tract 
of  fillet  to  the  brain ;  sp,  fibers  of  superior  peduncle  of  the  cere- 
bellum;  t',  fiber  of  crossed  pyramidal  tract;  ts,  point  of  decussation; 
v,  division  of  fiber  x  into  its  cranial  and  caudal  extensions ;  w,  a 
collateral  of  the  longitudinal  fiber  ir. 


198  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

Each  posterior  root  fiber  after  passing  into  the  cord  sepa- 
rates into  two  parts  one  of  which  extends  craniad,  the  other 
caudad  (Fig.  102).  Both  give  off  branches  at  right  angles, 
called  collaterals,  which  terminate  in  arborizations  about  the 
cells  of  the  cord. 

Each  nerve  cell  with  all  its  processes  is  called  a  neurone. 
It  presents  two  kinds  of  processes,  protoplasmic  processes 
or  dendrites  and  an  axis-cylinder  process  or  ax  one  (Fig. 
101).  The  dendrites,  except  in  the  ganglia  outside  of  the 
central  nervous  system,  are  usually  several  in  number  and 
comparatively  short,  while  there  is  but  one  axone  from  each 
cell,  which  may  be  more  than  a  foot  in  length.  A  number 
of  axones  (nerve  fibers),  each  of  which  is  surrounded  by  a 
sheath,  the  neurilemma,  constitutes  a  nerve  bundle  or  nerve. 
Every  axone  or  nerve  fiber  originates  in  a  cell,  but  termi- 
nates freely  either  within  the  central  nervous  system  or 
in  some  other  part  of  the  body  (Figs.  101,  102).  Within 
the  central  nervous  system  a  fiber  usually  ends  in  an 
arborescence  which  may  be  contiguous  but  not  continuous 
with  the  dendrites  of  another  cell.  The  nerve  processes 
have  the  power  of  conducting  impulses  whether  derived 
from  the  cell  itself  or  an  external  stimulus.  The  dendrites 
conduct  impulses  toward  the  cell,  while  the  axone  conducts 
them  from  the  cell. 

The  sensory  fiber  r  (Fig.  102)  leads  from  the  dermis  of 
the  cat's  paw.  A  pin-prick  in  the  paw  causes  an  impulse 
to  be  transmitted  along  the  fiber  to  the  cell  g,  and  thence  by 
its  axone,  x,  to  the  point  v  within  the  cord  where  the  fiber 
splits.  From  the  point  v  the  impulse  will .  proceed  both 
through  the  ascending  portion  of  the  fiber,  ir,  and  the  col- 
lateral, w.  By  the  latter  route  it  will  stimulate  the  cell  m, 
whose  axone  terminates  in  the  foreleg  muscles,  which  are 
thereby  made  to  contract  and  pull  the  paw  away  from  the 
irritating  object.  This  process  may  take  place  without  con- 


THE   NERVOUS   SYSTEM.  199 

sciousness,  and  is  then  known  as  reflex  action.  If,  how- 
ever, the  impulse  travels  along  the  fiber  ir,  and  thence 
through  the  fiber  ^  to  the  brain,  whence  an  impulse  de- 
scends through  the  fiber  t',  ts,  the  process  is  known  as  volun- 
tary reaction. 

THE  FIBER  TRACTS  OF  THE  CENTRAL 
NERVOUS  SYSTEM. 

As  before  stated,  the  white  matter  of  each  half  of  the 
cord  is  divided  by  the  exit  and  entrance  of  the  nerve  roots 
into  three  columns — anterior,  lateral,  and  posterior.  Each 
of  these  columns  is  subdivided  into  tracts  which  have  special 
names  and  special  functions  (Fig.  103). 

In  the  posterior  column  two  tracts  are  recognized:  the 
fasciculus  gracilis,  occupying  the  medial  third  of  the  column, 
and  the  fasciculus  cuneatus,  composing  the  remainder.  In 
the  medulla  of  the  cat  these  two  tracts  may  be  distin- 
guished by  the  unaided  eye  (Fig.  96).  They  are  here 
called  the  funiculi  of  Goll  and  Burdach,  or  funiculi  gracilis 
and  cuneatus.  Their  fibers  are  largely,  if  not  entirely,  the 
axones  of  the  ganglion  cells  on  the  posterior  roots  of  the 
spinal  nerves.  They  terminate  in  the  nuclei  gracilis  and 
cuneatus,  two  small  masses  of  nerve  cells  in  the  medulla 
laterad  of  the  fourth  ventricle  (Fig.  102).  That  these 
fibers  are  processes  of  the  spinal  ganglion  cells  is  proved 
by  the  fact  that  they  degenerate  if  the  posterior  nerve  roots 
are  severed  close  to  the  cord.  In  whales,  where  the  pelvic 
extremities  are  wanting,  the  fasciculi  gracilis  and  cuneatus 
are  very  small. 

The  lateral  column  is  composed  of  five  tracts :  the  direct 
cerebellar  tract,  the  antero-lateral  descending  cerebellar 
tract,  the  antero-lateral  ascending  cerebellar  tract  or  Gow- 
er's  tract,  the  lateral  ground  bundle,  and  the  crossed  pyra- 
midal tract. 


200 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


The  direct  cerebellar  tract  occupies  the  superficial  region 
of  the  cord  later  ad  of  the  posterior  cornu  of  gray  matter. 
Its  fibers  originate  from  the  cells  of 
the  more  central  portion  of  the  gray 
matter  throughout  the  cord  and  ter- 
minate in  the  cerebellum.  Its  fibers 
help  to  form  the  inferior  peduncle  of 
the  cerebellum. 

The  antcro-lateral  descending 
cerebellar  tract  occupies  the  super- 
ficial area  ventrad  of  the  anterior 
horn  of  gray  matter.  Its  fibers 
originate  in  the  cells  of  the  cerebel- 
lum and  extend  caudad  in  the  cord. 
The  ant ero -lateral  ascending  cere- 
bellar or  Gowers's  tract  occupies  the 
superficial  area  laterad  of  the  ante- 
rior horn.  Its  fibers  probably  origi- 
nate in  the  cells  of  central  gray 
matter  throughout  the  cord,  and 
largely  terminate  in  the  cerebellum. 
The  lateral  ground  bundle  consists 
largely  of  fibers  with  a  short  course, 
many  of  which  are  commissural,  con- 
necting the  two  halves  of  the  spinal 
cord. 

The  crossed,  pyramidal  tract  con- 
tains the  longest  fibers  of  any  of  the 
tracts  of  the  central  nervous  system 
and  occupies  a  large  area  just  lat- 
erad of  the  posterior  horn  of  gray 
matter.  Its  fibers  originate  in  the  cortical  cells  of  the  brain 
near  the  crucial  sulcus  (Fig.  92),  and  descend  as  part  of  the 
internal  capsule,  through  the  corpus  striatum  and  laterad  of 


FIG.    103.      DIAGRAM    OF 
SOME    FIBER     TRACTS. 
DORSAL  ASPECT. 

al,  Antero-lateral  ascend- 
ing cerebellar  tract;  c, 
posterior  corpus  quad- 
rigeminum ;  cer,  lateral 
lobe  of  cerebellum, 
whose  median  portion 
is  removed ;  eg,  the  two 
fasciculi  gracilis  and  cu- 
neatus  represented  as 
one;  cp,  crossed  pyra- 
midal or  chief  motor 
tract ;  cp' t  crossed  pyra- 
midal tract  in  the  re- 
gion of  the  cerebral 
peduncle ;  dc,  direct 
cerebellar  tract ;  fi,  the 
large  part  of  the  fillet 
derived  from  nc ;  nc, 
nuclei  gracilis  and  cu- 
neatus;  s,  decussation 
of  pyramidal  tracts ; 
x,  sensory  or  superior 
pyramidal  decussa- 
tion ;  sp,  superior  pe- 
duncle of  cerebellum. 


THE   NERVOUS    SYSTEM.  201 

the  optic  thalamus  to  the  base  of  the  brain.  Here  it  is  one 
of  the. three  main  tracts  forming  the  crus  or  peduncle  of  the 
cerebrum,  whence  it  extends  through  the  pons  Varolii,  ap- 
pearing along  the  median  ventral  line  of  the  medulla  as  the 
pyramid  (Fig.  93).  At  the  caudal  end  of  the  medulla  it 
crosses  dorsad  to  the  opposite  side  of  the  cord  to  occupy  the 
area  laterad  of  the  posterior  horn  of  gray  matter.  Its 
fibers  terminate  largely  in  arborizations  around  motor  cells 
of  the  cranial  nerves  in  the  brain,  and  the  cells  in  the  an- 
terior horn  of  gray  matter,  from  which  originate  the  motor 
fibers  for  the  muscles  of  the  body.  Therefore  it  is  ap- 
parent that  this  tract  controls  largely  the  muscular  activities 
of  the  entire  body  (Figs.  102,  103,  and  104).  The  cross- 
ing of  the  fibers  of  this  tract  in  the  caudal  region  of  the 
medulla  is  known  as  the  motor  decussation  or  the  decussa- 
tion  of  the  pyramidal  tract. 

The  limits  of  these  various  fiber  tracts  of  the  central 
nervous  system  cannot  be  determined  by  dissection.  They 
have  been  worked  out  largely  by  experimental  physiology 
and  pathology,  and  by  studying  their  embryonic  develop- 
ment when  the  fibers  of  different  tracts  are  seen  to  acquire 
their  sheaths  (neurilemmse)  at  different  periods.  The  por- 
tion of  a  nerve  fiber  separated  from  its  cell  degenerates,  so 
that  if  the  fibers  of  the  crossed  pyramidal  tract  were  in- 
jured by  accident  or  disease  in  the  region  of  the  medulla, 
all  that  part  of  the  tract  in  the  cord  would  degenerate,  in 
consequence  of  which  the  subject  would  suffer  paralysis. 

The  larger  portions  of  the  tracts  thus  far  described  have 
been  confined  to  the  cord,  while  the  remaining  tracts  to  be 
discussed  concern  chiefly  the  brain.  In  order  to  understand 
these  it  is  necessary  to  remember  that  the  cortex  of  the 
brain  is  composed  of  millions  of  nerve  cells  which  give 
origin  to  nerve  fibers  extending  to  other  portions  of  the 
cortex,  to  the  basal  ganglia,  the  cerebellum,  medulla,  and 


202  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

spinal  cord  (Fig.  104).  Likewise  some  of  the  fibers  origi- 
nating in  the  cells  of  the  cord,  medulla,  cerebellum,  and 
basal  ganglia  terminate  about  the  cells  of  the  cortex.  The 
cord,  medulla,  and  cerebellum  are  connected  with  the  higher 
brain  centers  by  the  fibers  of  the  cerebral  peduncles  (Figs. 
93  and  104).  Each  peduncle  is  separted  into  two  longi- 
tudinal parts  by  an  elongated  mass  of  gray  matter,  the 
substantia  nigra.  The  dorsal  part  is  known  as  the  teg- 
mentum,  while  the  ventral  part  is  the  crusta. 

The  fibers  of  the  brain  are  of  three  kinds — the  commis- 
sural  fibers,  the  projection  fibers,  and  the  association  fibers. 


7 


FIG.  104.    DIAGRAM  OF  CHIEF  FIBER  TRACT  OF  THE  MAMMALIAN  BRAIN. 
LATERAL  ASPECT. 

a,  b,  c,  d,  e,  Fibers  forming  internal  capsule ;  ac,  anterior  corpus  quad- 
rigeminum ;  cb,  direct  cerebellar  tract ;  cr,  crossed  pyramidal  or 
chief  motor  tract;  cs,  cortico-pontine  or  secondary  motor  tract;  m, 
middle  peduncle  of  cerebellum ;  ng,  nuclei  gracilis  and  cuneatus ;  n. 
decussation  of  crossed  pyramidal  tract ;  o,  optic  thalamus ;  oc,  optic 
chiasm ;  pc,  posterior  corpus  quadrigeminum ;  pons,  transverse  fibers 
of  pons  Varolii;  py,  pyramids  formed  by  pyramidal  tract;  rn, 
nucleus  ruber;  s,  antero-lateral  cerebellar  tract;  sn,  substantia 
nigra;  sp,  superior  cerebellar  peduncle;  st,  corpus  striatum;  t,  fibers 
of  the  fillet  or  great  sensory  tract. 

The  commissural  fibers  constitute  the  commissures  of  the 
brain  previously  described  (Figs.  93,  95).  In  addition  to 
these  commissures,  numerous  other  fibers  cross  to  the 


THE   NERVOUS   SYSTEM.  203 

opposite  half  in  that  portion  of  the  brain  caudad  of  the 
optic  thalami.     The  internal  portion  of  the  medulla  ob— 
longata  possesses  numerous  transverse  fibers  which,  with 
the  longitudinal  fibers,  form  a  kind  of  reticulum  in  the  midst 
of  the  gray  matter,  known  as  the  formatio  reticularis. 

The  projection  fibers  (Fig.  104)  are  those  connecting  the 
cortex  with  the  lower  brain  centers  and  the  cord.  The  chief 
motor  tract  is  the  crossed  pyramidal  tract  already  described 
in  the  cord.  It  may  be  traced  from  the  pyramids  to  its 
origin  in  the  cortex  in  the  region  of  the  crucial  sulcus  (Fig. 
92),  by  slicing  away  the  ventral  portion  of  the  brain 
obliquely  in  a  plane  joining  the  cranial  margin  of  the  pons 
and  the  crucial  sulcus.  Numerous  fibers  are  given  off  by 
this  tract  to  the  motor  roots  of  the  cranial  as  well  as  the 
spinal  nerves. 

The  secondary  motor  tract,  cortico  pontine  tract,  carries 
motor  impulses  from  the  frontal  cortex  to  the  medulla, 
whence  other  fibers  convey  them  to  the  opposite  half  of  the 
cerebellum.  The  axis-cylinders  of  the  cells  here  transmit 
the  impulses  through  the  inferior  peduncle  to  the  cells  in  the 
anterior  horn  of  gray  matter  of  the  cord. 

The  great  sensory  tract  of  the  brain  is  the  fillet.  Its 
fibers  originate  largely  in  the  cells  of  the  nuclei  gracilis 
and  cuneatus  of  the  medulla  (Figs.  102,  103,  104)  and  cross 
over  to  the  opposite  side  of  the  medulla,  forming  the  sensory 
or  superior  pyramidal  decussation.  This  tract  receives  also 
fibers  from  the  spinal  cord,  the  cerebellum,  and  the  medulla 
oblongata. 

These  projection  fibers,  after  leaving  the  peduncular 
region,  turn  dorsad  to  pass  with  others  through  the  corpus 
striatum  and  laterad  of  the  optic  thalamus.  In  this  part  of 
their  course  they  form  what  is  known  as  the  internal  capsule 
(Fig.  98).  The  spreading  out  of  the  projection  fibers  just 
beneath  the  cortex  of  the  cerebrum  forms  the  corona 
radiata. 


204  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

The  association  fibers  are  those  which  connect  different 
portions  of  the  same  cerebral  hemisphere.  Two  kinds  are 
recognized.  The  short  fibers  connect  adjacent  convolu- 
tions, while  the  long  ones  place  in  communication  two  re- 
mote portions  of  a  hemisphere. 

PRACTICAL  QUESTIONS  AND  SUGGESTIONS. 

1.  Describe  the  membranes  of  the  cord. 

2.  What  difference  in  the  size  of  the  nerve  roots  in  the  various 
regions  of  the  cord? 

3.  Draw  a  cross-section  of  the  cord  showing  all  features  visible  to 
the  naked  eye. 

4.  How  does  the  arrangement  of  the  gray  matter  of  the  cord  and 
brain  differ? 

5.  Describe  the  processes  of  nerve  cells. 

6.  In  what  portions  of  the  body  are  nerve  cells  found? 

7.  What  is  the  location  of  the  cells  whose  protoplasmic  processes 
largely  make  up  the  fasciculi  cuneatus  and  gracilis. 

8.  What  part  of  the  cord  is  occupied  by  the  chief  motor  tract? 

9.  What  tracts  of  the  cord  originate  or  terminate  within  the  cere- 
bellum? 

10.  Describe  the  course  of  the  crossed  pyramidal  tract  throughout 
the  axial  nervous  system. 

11.  Describe  three  bundles  of  commissural  fibers  in  the  brain. 

12.  Which  tract  of  the  projection  fibers  contains  the  longest   axones? 

13.  Describe  the  great  sensory  tract  of  the  brain. 

14.  What  do  the  association  fibers  connect? 

15.  Tell  what  is  known  of  the  functions  of  various  regions  of  the 
cortex. 

16.  Explain  why  paralysis  of  the  left  side  of  the  body  would  result 
from  an  injury  to  the  right  motor  region  of  the  cortex. 

17.  Procure  a  piece  of  spinal  cord  from  the  butcher-shop.      Smear 
a  bit  of  the  gray  matter  on  a  glass  slip,  dry,  then  stain  in  hematoxylin, 
wash,  and  after  drying  mount  in  balsam.      Draw  and  describe  nerve 
cells  thus  found. 

THE  PERIPHERAL  NERVES. 

All  portions  of  the  head,  trunk,  and  limbs  of  the  cat  are 
supplied  with  nerve  fibers  which  are  in  communication  with 
the  central  nervous  system  by  means  of  fifty-two  pairs  of 


THE   NERVOUS   SYSTEM. 


205 


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206  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

nerve  bundles,  forming  what  are  known  in  the  brain  region 
as  the  cranial  nerves  and  in  the  region  of  the  cord  as  the 
spinal  nerves. 

The  Cranial  Nerves. — There  are  twelve  pairs  of  cranial 
nerves,  all  of  which  pass  through  foramina  in  the  base  of 
the  skull,  and  all  except  one,  the  tenth  or  vagus,  are  dis- 
tributed to  structures  of  the  head  and  neck.  They  are 
divided  according  to  function  into  motor  and  sensory. 
Some  of  the  nerves  communicate  with  the  brain  by  more 
than  one  root,  and  in  such  cases  the  same  nerve  may  have 
sensory  fibers  in  one  root  and  motor  fibers  in  another.  For 
example,  the  trigeminal  nerve  transmits  a  stimulus  causing 
the  muscles  of  mastication  to  contract  and  also  supplies  the 
teeth  with  sensory  fibers  (Fig.  93). 

The  olfactory,  optic  and  auditory  are  the  only  cranial 
nerves  wholly  sensory.  The  oculomotor,  patheticus  or 
trochlearis,  abducens,  spinal  accessory,  and  hypoglossal  are 
wholly  motor.  The  trigeminal,  facial,  glossopharyngeal 
and  vagus  contain  both  motor  and  sensory  fibers. 

The  dissection  of  the  cranial  nerves  is  very  difficult.  A 
head,  containing  a  brain  hardened  by  a  formalin  injection, 
should  be  placed  in  500  c.c.  of  5%  nitric  acid,  which  will 
decalcify  the  bone  in  about  a  week.  After  washing  out  the 
acid  by  soaking  the  specimen  in  running  water  twenty-four 
hours,  the  dissector  may  with  much  care  follow  the  course 
of  the  nerves  peripherad  from  their  origin  at  the  base  of  the 
brain.  The  vagus  nerve  must  of  course  be  traced  in  an 
entire  specimen,  where  it  may  be  easily  followed  in  the 
neck  region  along  with  the  carotid  artery,  whence  it  passes 
to  the  lungs  and  stomach  (Fig.  66). 

Some  of  the  sensory  nerve  roots  bear  ganglia,  the  largest 
of  which  is  the  Gasserian  ganglion,  more  than  a  half  centi- 
meter in  diameter,  forming  a  knot  on  the  sensory  root  of 
the  trigeminal,  within  the  cranial  cavity  (Fig.  93). 


THE   NERVOUS   SYSTEM.  207 

The  Spinal  Nerves. — There  are  forty  pairs  of  nerves 
connected  with  the  spinal  cord.  They  issue  from  the 
vertebral  canal  through  the  intervertebral  foramina.  Each 
nerve  is  connected  to  the  cord  by  a  ventral  and  dorsal  root 
(Figs.  93  and  102).  The  former  is  also  known  as  the 
motor  root,  since  its  fibers  are  almost  entirely  motor,  while 
the  latter  is  the  sensory  root,  as  it  is  composed  of  fibers 
transmitting  impulses  to  the  central  nervous  system.  A 
ganglion  about  the  size  of  a  pinhead  is  located  on  the  dorsal 
root  immediately  proximad  of  its  junction  with  the  ventral 
root,  within  the  intervertebral  foramen.  This  anatomy  can 
be  displayed  by  cutting  away  the  dorsal  muscles  on  either 
side  of  the  column,  and  then,  with  the  bone-cutters,  severing 
the  laminae  of  several  of  the  arches  of  the  vertebras,  so  that 
the  roof  may  be  removed  from  the  vertebral  canal  (Fig. 
22). 

Immediately  beyond  the  intervertebral  foramen  each 
nerve  gives  off  a  dorsal  branch  to  the  muscles  of  the  back, 
and  a  small  connecting  twig  to  the  sympathetic  system. 
The  main  nerve  is  then  spoken  of  as  the  ventral  branch. 
These  main  nerves  or  ventral  branches,  in  various  regions 
of  the  trunk,  anastomose  with  each  other,  forming  plexuses. 
In  the  region  of  the  neck  there  is  formed  the  cervical  plexus; 
in  the  region  of  the  shoulder,  the  brachial  plexus;  in  the 
region  of  the  loins,  the  lumbar  plexus;  and  in  the  region  of 
the  sacrum,  the  sacral  plexus  (Figs.  105  and  106). 

There  are  eight  cervical  nerves,  the  first  of  which  does 
not  make  its  exit  through  the  intervertebral  foramen,  as  do 
all  the  other  spinal  nerves,  but  traverses  a  foramen  in  the 
atlas.  The  first  five  cervical  nerves,  the  three  posterior 
cranial  nerves,  and  branches  from  the  sympathetic  trunk, 
form  the  cervical  plexus.  These  five  cervical  nerves 
supply  mainly  the  structures  of  the  neck. 

There  are  thirteen  pairs  of  thoracic  nerves.     The  ventral 


208 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


branches  of  the  sixth,  seventh,  and  eighth  cervical  nerves 
and  the  first  thoracic  nerve  form  the  brachial  plexus. 
This  may  be  displayed  by  removing  the  cephalo-humeral 
muscle  and  cutting  through  the  pectoral  muscles  about  two 


FIG.  105.    VENTRAL  ASPECT  OF  THE  BRACHIAL  PLEXUS  AND  CHIEF  NERVES 

OF  THE  ARM. 

6,  7,  8  and  i,  Sixth,  seventh,  and  eighth  cervical  and  first  dorsal  nerves ; 
at,  ath,  anterior  thoracic  nerves ;  a  and  b,  to  muscles  of  the  forearm ; 
c  and  d,  to  the  joint;  ex,  circumflex  nerve;  cu,  internal  cutaneous; 
de,  to  the  deltoid ;  g,  to  the  digits ;  /,  to  the  digits ;  fo,  supracondy- 
loid  foramen;  It,  long  thoracic;  me,  musculocutaneous ;  me,  median 
nerve;  pi,  posterior  interosseous ;  pth,  posterior  thoracic;  sp,  mus- 
culospiral;  sp,  to  suprascapular  region;  sb,  to  subscapular  region; 
sx,  subscapular ;  ra,  radial ;  un,  ulnar  nerve. 


THE   NERVOUS   SYSTEM.  209 

centimeters  from  their  origin  (Fig.  47).  The  manner  in 
which  the  nerves  anastomose  varies  somewhat,  but  the  fol- 
lowing will  be  found  approximately  correct: 

The  sixth  cervical  nerve  gives  off  a  small  branch  to  the 
rhomboideus  and  levator  anguli  muscles  of  the  shoulder, 
and  then  divides  into  two  nearly  equal  branches,  one  of 
which  supplies  the  muscles  on  the  lateral  aspect  of  the 
scapula,  and  the  other  joins  with  the  seventh  cervical  nerve. 
Small  branches  from  the  fifth  and  sixth  cervical  nerves 
unite  to  form  the  phrenic  nerve  supplying  the  diaphragm. 

The  seventh  cervical  nerve  gives  off  three  small  branches 
at  about  the  same  point,  one  of  which  is  the  posterior 
thoracic  supplying  the  serratus  magnus  muscle,  a  second 
helps  to  form  the  musculocutaneous,  and  the  third  forms 
part  of  the  median  and  anterior  thoracic.  The  main  por- 
tion of  the  seventh  cervical  unites  with  the  eighth  and  first 
thoracic,  to  form  the  musculospiral  nerve.  The  circumflex 
and  subscapular  branches  supplying  the  deltoid  and  sub- 
scapular  muscles  are  also  derived  from  the  seventh. 

The  eighth  cervical  nerve,  after  giving  off  a  small  branch 
to  the  pectoral  muscle,  a  small  twig  to  the  median  nerve, 
and  a  large  branch  to  the  first  thoracic  nerve,  is  continued 
as  the  main  part  of  the  musculospiral  nerve. 

The  first  thoracic  nerve  gives  first  a  large  branch  to  the 
musculospiral  nerve,  a  second  small  branch  to  the  anterior 
thoracic,  and  a  third  branch  forming  the  internal  cutaneous 
nerve  supplying  the  skin  of  the  arm  and  forearm  on  the 
caudal  aspect.  The  main  portion  of  the  first  thoracic  nerve 
then  continues  as  the  main  part  of  the  ulnar  nerve. 

The  nerves  of  the  forelimb  are  five  in  number  (Fig. 
105)  :  the  external  cutaneous  or  musculo-cutaneous,  the  in- 
ternal cutaneous,  the  musculospiral,  the  median,  and  the  ul- 
nar. The  external  cutaneous  arises  from  the  sixth  and 
seventh  cervical  nerves  and  passes  distad  along  the  caudal 
19 


210  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

aspect  of  the  biceps  to  the  cranial  aspect  of  the  forearm, 
where  it  becomes  subcutaneous.  It  supplies  the  biceps  and 
coracoid  muscles  and  the  skin  of  the  forearm.  The  internal 
cutaneous  arises  from  the  first  thoracic  and  passes  along  the 
ventral  side  of  the  arm,  becoming  subcutaneous  just  proxi- 
mad  of  the  elbow,  where  it  is  distributed  to  the  skin  of  the 
'arm  and  forearm  on  the  caudal  and  ventral  aspects. 

The  musculo  spiral  arises  from  the  seventh  and  eighth 
cervical  and  first  thoracic  nerves.  It  is  the  largest  com- 
ponent of  the  brachial  plexus.  It  winds  obliquely  around 
the  humerus  to  the  cranial  aspect,  where  it  divides  into  two 
branches,  the  radial  and  the  posterior  interosseous.  The 
radial  nerve  is  the  smaller  and  becomes  subcutaneous  near 
the  elbow,  and  passes  along  the  radial  region.  The  pos- 
terior interosseous  proceeds  along  the  dorsal  aspect  of  the 
forearm  to  the  wrist,  where  it  divides  into  branches  supply- 
ing the  digits. 

The  median  nerve  arises  from  the  seventh  and  eighth 
cervical  and  first  thoracic.  It  follows  the  course  of  the 
brachial  artery,  passing  through  the  supracondylar  foramen 
to  the  elbow,  where  it  passes  beneath  the  pronator  teres  to 
the  carpal  region,  and  supplies  the  first,  second,  and  third 
digits.  It  also  supplies  the  pronator  teres  and  flexor 
muscles  of  the  forearm. 

The  ulnar  nerve  (Fig.  105)  is  derived  from  the  eighth 
cervical  and  first  thoracic.  It  courses  with  the  brachial 
artery  to  the  middle  of  the  humerus,  where  it  turns  caudad 
to  pass  between  the  olecranon  process  and  internal  condyle 
of  the  humerus.  It  is  here  subcutaneous  and  furnishes  the 
sensation  experienced  when  one  strikes  what  is  popularly 
called  his  "  funny  bone,"  but  what  is  really  the  ulnar  nerve. 
It  then  passes  down  the  ulnar  side  of  the  forearm,  supply- 
ing some  of  the  flexor  muscles,  and  finally  divides  to  supply 
the  fourth  and  fifth  digits.  The  ventral  branches  of  the 


THE   NERVOUS    SYSTEM.  211 

remaining  thoracic  nerves  encircle  the  body,  supplying  the 
muscles  and  skin  of  those  regions. 

The  lumbar  plexus  (Fig.  106)  is  composed  of  the  an- 
astomosing of  the  ventral  branches  of  the  four  caudal  lum- 
bar nerves.  As  in  the  cervical  and  thoracic  nerves,  the 
lumbar  nerves  divide  into  dorsal  and  ventral  branches  im- 
mediately without  the  intervertebral  foramen.  The  former 
supply  the  muscles  and  skin  of  the  back.  In  order  to  dis- 
play the  lumbar  nerves,  the  entire  ventral  and  lateral 
abdominal  wall  should  be  cut  away  and  the  specimen 
securely  nailed  to  the  tray  on  its  back.  The  adipose  tissue 
and  muscles  lying  on  either  side  of  the  bodies  of  the  lumbar 
vertebrae  must  be  carefully  picked  away  until  the  roots  of 
the  nerves  are  apparent.  They  may  then  be  easily  followed 
distad. 

The  first  three  lumbar  nerves  of  the  cat  are  represented 
in  man  by  the  ilio-hypogastric  and  ilio-inguinal.  The  first 
nerve  supplies  the  rectus  muscle  and  skin  of  the  abdomen. 
This  nerve  and  the  two  next  described  are  scarcely  as  large 
in  diameter  as  an  ordinary  pin.  The  ventral  branch  of  the 
second  lumbar  nerve  divides  into  two  branches,  and  sup- 
plies the  skin  of  the  caudal  part  of  the  abdomen,  and  struc- 
tures in  the  inguinal  region.  The  ventral  branch  of  the 
third  lumbar  nerve  supplies  the  inguinal  region  and  is  also 
distributed  to  the  transverse  and  rectus  muscles.  The 
fourth  lumbar  nerve  divides  into  two  parts,  one  of  which  is 
the  genito-crural  nerve,  supplying  the  skin  and  other  struc- 
tures of  the  ventral  abdominal  wall  and  thigh,  the  other 
branch  together  with  part  of  the  fifth  nerve  forms  the  ex- 
ternal cutaneous,  supplying  the  lateral  surface  of  the  thigh 
region. 

The  anterior  crural  nerve  is  composed  mainly  of  branches 
of  the  fifth  and  sixth  lumbar.  It  receives  a  small  branch 
from  the  fourth.  It  supplies  the  psoas  muscles,  which  it 


212  ELEMENTS    OF   MAMMALIAN   ANATOMY. 


FIG.  1 06.    VENTRAL  ASPECT  OF  THE  NERVES  OF  HIND-LIMB. 

4,  5,  6,  7,  i,  2,  and  3,  Fourth,  fifth,  sixth,  and  seventh  lumbar,  and  first, 
second,  and  third  sacral  nerves ;  a,  branch  from  the  fourth  to  the 
fifth ;  ac,  anterior  crural ;  en,  saphenous ;  d,  anterior  tibial ;  e, 
peroneal  or  musculocutaneous ;  ex,  external  popliteal  or  peroneal ; 
ef,  external  plantar ;  jo,  obturator  foramen ;  gs,  greater  sciatic ;  g, 
genito-crural ;  it,  internal  popliteal ;  ip,  internal  plantar ;  kn, 
knee ;  /,  external  cutaneous  ;  Is,  lumbosacral  cord ;  t,  posterior  tibial : 
s,  small  sciatic. 


THE   NERVOUS   SYSTEM.  213 

pierces,  and  then  divides  into  several  branches,  one  of  which 
is  the  saphenous,  passing  subcutaneously  along  the  medial 
aspect  of  the  leg.  The  other  nerves  supply  the  muscles  of 
the  thigh  on  the  cranial  and  medial  aspect.  The  obturator 
nerve  is  composed  of  branches  from  the  sixth  and  seventh 
lumbar.  It  is  smaller  than  the  preceding,  and  passes 
through  the  obturator  foramen  to  supply  the  obturator,  ad- 
ductor, gracilis  and  pectineus  muscles. 

The  sacral  plexus  is  formed  of  the  three  sacral  nerves 
with  branches  from  the  sixth  and  seventh  lumbar  nerves. 

The  great  sciatic  nerve  is  composed  mainly  of  the  ventral 
branches  of  the  seventh  lumbar  and  first  sacral  nerves.  It 
usually  receives  accessions  from  the  other  sacral  nerves  and 
the  sixth  lumbar.  The  great  sciatic  is  the  largest  peripheral 
nerve  in  the  body.  It  passes  caudad  from  its  origin  around 
the  greater  sciatic  notch  and  thence  along  the  caudal  aspect 
of  the  thigh  to  the  popliteal  space,  where  it  divides  into  the 
internal  and  external  popliteal  nerves.  The  former  con- 
tinues down  the  caudal  side  of  the  tibia  as  the  posterior 
tibial  nerve  to  the  internal  malleolus,  where  it  divides  into 
internal  and  external  plantar  nerves,  which  supply  the  digits. 
The  external  popliteal  or  peroneal  nerve  extends  to  the  outer 
cranial  aspect  of  the  leg,  where  it  divides  into  the  musculo- 
cutaneons  and  anterior  tibial  nerves.  The  former  extends 
between  the  extensor  longus'digitorum  and  peronei  muscles 
to  its  ramification  on  the  dorsum  of  the  foot.  It  supplies 
the  skin  along  its  course  and  the  peronei  muscles.  The 
anterior  tibial  nerve  passes  down  on  the  cranial  aspect  of 
the  tibia  beneath  the  extensor  longus  digitorum  muscle  to 
the  tarsal  region,  where  it  anastomoses  with  a  branch  of  the 
external  cutaneous,  and  supplies  the  skin,  tibialis  anticus, 
and  the  extensor  muscles. 

The  lesser  sciatic  nerve  comes  chiefly  from  the  second  and 
third  sacral  nerves.  It  supplies  the  region  of  the  anus  and 
the  biceps  muscle. 


214  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

Other  nerves  given  off  from  the  sacral  plexus  are  the 
glutei  and  pudic  nerves  supplying  the  buttock  muscles  and 
external  genital  organs. 

THE  SYMPATHETIC  NERVOUS  SYSTEM. 

The  sympathetic  nervous  system  is  composed  chiefly  of  a 
pair  of  nerve-cords  extending  from  the  base  of  the  skull  to 
the  root  of  the  tail,  a  number  of  ganglia  and  branches 
supplying  the  thoracic  and  abdominal  viscera,  and  numerous 
minute  fibers  supplying  the  muscular  walls  of  the  blood- 
vessels in  all  parts  of  the  body.  The  sympathetic  system 
supplies  all  non-striped  or  involuntary  muscles  in  any  part 
of  the  body.  The  two  branches  connecting  each  spinal 
nerve  with  a  sympathetic  nerve  cord  are  called  rami  com- 
municantes. 

In  order  to  demonstrate  this  system  successfully,  one 
should  use  a  lean  injected  specimen.  After  the  cat  has  been 
securely  nailed  on  its  back  to  the  tray,  the  entire  ventral  half 
of  the.  thoracic  and  abdominal  walls  should  be  removed. 
By  pushing  the  heart  and  lungs  to  the  left  side  a  white  cord 
about  one  millimeter  in  diameter  may  be  seen  lying  near  the 
median  dorsal  line  (Fig.  107) .  The  left  cord  may  be  found 
in  a  similar  manner  and  both  followed  craniad  and  caudad, 
noting  their  numerous  branches  in  accordance  with  the  fol- 
lowing description. 

The  sympathetic  nerve-cord  begins  in  the  superior  cer- 
vical ganglion  lying  near  the  angle  of  the  mandible,  beneath 
the  submaxillary  and  lymphatic  glands.  This  ganglion  is 
about  the  shape  of  a  grain  of  wheat,  but  not  more  than  half 
so  large,  and  is  adjacent  to  the  small  vagus  ganglion  on  the 
dorsal  side  of  the  carotid  artery.  The  ganglia  are  masses 
of  large  nerve  cells  and  occur  at  regular  intervals  on  the 
sympathetic  cords  in  the  body  cavity,  and  are  present  also  on 
some  of  the  branches  of  the  cords  (Fig.  108).  On  the 


THE   NERVOUS    SYSTEM. 


2I5 


cords  there  are  three  pairs  of  cervical  ganglia,  thirteen  pairs 
of  thoracic  ganglia,  seven  pairs  of  lumbar  ganglia,  and  one 
or  two  pairs  of  sacral  ganglia,  in  addition  to  two  median 
unpaired  sacral  ganglia. 

In  the  cervical  region  the 
sympathetic  and  vagus,  or 
tenth  cranial  nerve,  are 
bound  in  a  common  sheath 
lying  along  the  lateral  aspect 
of  the  carotid  artery.  One 
or  two  centimeters  craniad 
of  the  first  rib  is  the  thyroid 
or  middle  cervical  ganglion, 
whence  the  nerve  proceeds 
in  two  cords,  enclosing  the 
subclavian  artery,  to  the 


FIG.  107.  CHIEF  PART  OF  LEFT 
HALF  OF  SYMPATHETIC  SYSTEM 
CRANIAD  OF  THE  DIAPHRAGM. 
Semidiagrammatic. 

5,  6,  7,  8,  9,  and  ip,  Fifth,  sixth, 
seventh  and  eighth  cervical 
nerves,  and  first  and  second 
thoracic  spinal  nerves;  a,  the 
dorsal  branch  of  the  left  vagus 
In ;  an,  dorsal  branch  of  the  right 
vagus  ;  ax,  common  dorsal  vagus 
formed  by  a  and  an  ;  avb,  ventral 
vagus ;  be,  cardiac  branch  of  sg, 
cr,  carotid  plexus;  car,  carotid 
artery;  cm,  rami  communi- 
cantes;  cp,  cardiac  plexus;  dia, 
diaphragm;  g,  ganglia  in  the 
thoracic  cavity ;  ig,  middle  cer- 
vical ganglion ;  Ig,  portion  of 
left  lung;  In,  left  vagus  nerve; 
nv,  cranial  nerve;  pn,  phrenic 
nerve;  pp,  pulmonary  plexus; 
sn,  sympathetic  cord;  sm,  supe- 
rior cervical  ganglion;  sb,  left 
subclavian  artery;  sg,  stellate 
ganglion  or  inferior  cervical ; 
spm,  splanchnic  major  nerve; 
vg>  vagus  ganglion;  v,  vagus 
nerve. 


m 


w 


'til 


216  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

large  inferior  cervical  ganglion  just  caudad  of  the  first  rib. 
From  the  cervical  portions  of  the  sympathetic  cord  are 
given  off  numerous  delicate  branches,  forming  the  carotid 
plexus  on  the  carotid  artery,  and  uniting  with  the  eight 
posterior  cranial  nerves  and  the  first  spinal  nerve.  From 
the  inferior  cervical  ganglion  a  branch  goes  to  the  vagus 
nerve,  several  branches  to  the  brachial  plexus,  and  a  branch 
to  the  heart,  forming  the  cardiac  plexus,  while  the  main 
sympathetic  cord  continues  along  the  dorsal  thoracic  wall. 
A  ganglion  occurs  opposite  each  vertebral  body,  from  which 
it  gives  off  a  branch  to  the  corresponding  spinal  nerve.  The 
great  splanchnic  arises  from  the  main  cord  just  craniad  of 
the  diaphragm  and  extends  to  a  group  of  ganglia  in  the 
region  of  the  trunk  of  the  coeliac  axis  (Figs.  107  and  108). 
These  ganglia  and  anastomosing  branches  constitute  the 
solar  or  epigastric  plexus,  lying  dorsad  of  the  stomach,  to 
which  it  sends  numerous  branches.  This  plexus  also  receives 
the  lesser  splanchnic  nerve  coming  from  the  sympathetic  cord 
just  craniad  of  the  diaphragm,  and  branches  from  the  tenth 
cranial  nerve. 

The  largest  ganglion  of  the  solar  plexus  is  the  semilunar. 
The  solar  and  its  allied  plexuses  send  nerves  to  the  dia- 
phragm, suprarenal  bodies,  many  of  the  blood-vessels  of  the 
abdominal  cavity,  stomach,  kidneys,  ureters,  testes  or 
ovaries,  uterus,  liver,  gall-bladder,  spleen,  pancreas,  and 
intestines. 

The  hypogastric  plexus  is  the  third  great  sympathetic 
plexus.  It  lies  on  the  ventral  aspect  of  the  two  caudal 
lumbar  vertebrae  and  is  formed  by  branches  from  the  solar 
plexus  and  a  few  twigs  from  the  sympathetic  cords.  It  sup- 
plies the  blood-vessels  of  the  pelvic  region  and  all  the 
organs  of  the  pelvis.  The  sympathetic  cords  in  the  lumbar 
region  lie  near  together  and  the  communicating  branches 
between  them  and  the  spinal  nerves  are  longer  than  in  the 


THE   NERVOUS    SYSTEM. 


317 


thoracic  region.  In  the  sacral  region  there  are  no  rami 
communicantes,  and  the  ganglia  are  irregularly  arranged. 
A  median  ganglion  in  the  sacral  region  is  known  as  the 
ganglion  impar.  There  may  be  two  median  ganglia.  The 
sympathetic  cords  terminate  in  the  tail. 


b? 


FIG.  108.  CHIEF  PART  OF  LEFT  HALF  OF  SYMPATHETIC  SYSTEM  CAUDAD 
OF  THE  DIAPHRAGM.      Semidiagrammatic. 

bl,  Bladder ;  ce,  cceliac  axis ;  du,  duodenum  cut  off ;  dia,  diaphragm ;  gr, 
anterior  gastric  plexus;  g,  ganglion;  im,  inferior  mesenteric  artery; 
il,  external  iliac  artery;  ng,  dorsal  branch  of  vagus  (Fig.  103,  ax}  ; 
nl,  ventral  branch  of  vagus;  oe,  esophagus  cut  off;  p,  superior  mesen- 
teric plexus;  plx,  inferior  mesenteric  plexus;  px,  branches  to  dorsal 
gastric  plexus ;  rn,  renal  plexus ;  sm,  superior  mesenteric  artery ; 
spn,  splanchnic  major  or  greater  splanchnic  nerve  from  the  sym- 
pathetic cord ;  sg,  semilunar  ganglion ;  spc,  sympathetic  cord'  of  left 
side. 


20 


2i8  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

PRACTICAL   QUESTIONS    AND    SUGGESTIONS. 

1.  Name  the  foramina  of  the  skull  giving  passage  to  one  or  more 
cranial  nerves. 

2.  From  a  study  of  one  or  more  specimens  and  the  description  in 
the  book  make  a  diagrammatic  drawing  of  each  cranial  nerve. 

3.  Which  cranial  nerves  have  their  roots  in  the  medulla? 

4.  Name  the  cranial  nerves  which  are  wholly  motor. 

5.  Which  of  the  cranial  nerves  do  not  supply  structures  of  the  head? 

6.  Of  what  are  ganglia  composed? 

7.  Make  a  drawing  of  your  dissection  showing  the  connection  be- 
tween the  spinal  and  sympathetic  nerves. 

8.  Which  spinal  nerves  form  the  several  plexuses? 

9.  Make  a  drawing  showing  wherein  the  brachial  plexus  in  your 
specimen  differs  from  that  described  in  the  text. 

10.  Write   a  description   of  your   dissection   of  the   nerves   of  the 
thoracic  limb. 

11.  Mention  in  what  way  the  lumbar  plexus  differs  from  the  descrip- 
tion in  the  book. 

12.  Draw  the  great  sciatic  nerve  and  its  branches  as  seen  from  the 
caudal  aspect. 

13.  What  nerves  supply  the  digits? 

14.  Describe  the  chief  plexuses  of  the  sympathetic  system. 

15.  How  do  stimuli  from  the  viscera  reach  the  brain? 

16.  What  portion  of  the  body  is  not  supplied  with  nerves  from  the 
sympathetic  system? 

THE  ORGANS  OF  SENSE. 

The  organs  of  sense  are  the  specialized  peripheral  termi- 
nations of  the  sensory  nerves,  and  are  so  constructed  as 
to  be  capable  of  receiving  only  a  certain  kind  of  stimulus. 
The  stimuli  for  the  eye  are  ether  vibrations;  those  for  the 
ear  are  vibrations  of  the  air.  The  stimulation  of  the  sen- 
sory nerves  produces  sensations  in  the  cells  of  the  cerebral 
cortex  to  which  they  lead. 

The  external  stimuli  giving  rise  to  the  internal  sensations 
of  seeing,  hearing,  smelling,  and  tasting  are  transmitted  by 
only  four  pairs  of  cranial  nerves,  while  the  stimuli  of  cu- 
taneous sensations  are  transmitted  by  three  pairs  of  cranial 
nerves  and  all  the  spinal  nerves. 


THE   NERVOUS    SYSTEM. 


219 


Cutaneous  Sense  Organs. — The  cutaneous  sense  organs 
are  composed  of  the  endings  of  the  sensory  nerves  in  all 
parts  of  the  skin  and  the  mucous  membrane  of  the  mouth, 
nose,  arms,  vagina,  and  urethra.  One  kind  of  sense  organs, 
those  of  pain,  are  present  in  every  organ  of  the  body.  The 
sense  organ  of  pain  is  probably  an  unmodified  free  nerve- 
ending. 

While  all  portions  of  the  skin  and  perhaps  other  parts 
of  the  body  are  supplied  with  organs  capable  of  receiving 
stimuli  giving  rise  to  tactile  sensation,  the  soles  of  the  feet 
and  the  skin  at  the  base  of  the  vibrissae  are  specially  sensi- 
tive regions.  The  nerves  terminate  in  a  kind  of  wreath 
formation  about  the  base  of  the  vibrissae. 

All  of  these  sense  organs  are  invisible  to  the  naked  eye 
except  the  Pacinian  corpuscles.  If  the  mesentery  is  held 
up  and  looked  through  toward  the 
light,  the  Pacinian  corpuscles  or  sen- 
sory nerve  terminations  appear  as 
translucent  oval  bulbs  about  two  milli- 
meters long.  If  a  piece  of  the  mesen- 
tery containing  a  corpuscle  is  pinned 
tense  on  a  piece  of  cork  and  then  cut 
out  and  placed  ten  minutes  in  3% 
acetic  acid,  the  termination  of  the  nerve 
within  the  corpuscle  may  be  seen  with 
a  microscope  magnifying  thirty  diam- 
eters. All  the  spinal  sensory  nerve 
fibers  enter  the  cord  by  the  posterior 
root  (Figs.  93  and  100). 

The  Olfactory  Organ. — The  organ 
of  smell  lies  in  that  part  of  the  mucous 
membrane  lining  the  caudal  part  of  the  nasal  cavity  and  the 
basal  third  of  the  ethmoturbinal  bones   (Fig.   18).     That 
part  of  the  mucous  membrane  containing  the  olfactory  cells 


FIG.  109.  PACINIAN 
CORPUSCLE  FROM 
THE  MESENTERY.  X 
20. 

ax,  Axis-cylinder ;  n, 
neurilemma ;  m,  the 
white  substance  of 
Schwann ;  e,  epithe- 
lial cell. 


220  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

is  known  as  the  Schneiderian  membrane.  In  a  fresh  speci- 
men it  is  of  a  grayish  color  while  the  other  mucous  mem- 
brane is  red.  The  first  pair  of  cranial  nerves  convey  the 
olfactory  impulse  to  the  brain.  They  pass  through  the  fora- 
mina in  the  cribriform  plate  of  the  ethmoid  bone,  to  the 
olfactory  bulbs,  from  each  of  which  two  roots  extend  to  the 
.base  of  the  cerebrum  (Fig.  93). 

The  Gustatory  Organ. — The  organ  of  taste  is  located 
chiefly  in  the  mucous  membrane  on  the  dorsum  of  the 
tongue,  the  soft  palate,  the  pillars  of  the  fauces,  epiglottis, 
and  part  of  the  cheek.  On  the  dorsum  of  the  tongue  are 
seen  four  kinds  of  papillae — the  circumvallate,  the  fungi- 
form,  the  filiform,  and  flat.  The  circumvallate  papillae  are 
from  eight  to  twelve  in  number,  forming  two  sides  of  a 
triangle  on  the  caudal  portion  of  the  dorsum  of  the  tongue. 
The  fungi  form  are  blunt  papillae  scattered  sparsely  in  the 
midst  of  the  numerous  filiform  or  pointed  papillae  (Fig.  56). 
The  special  organs  of  taste,  known  as  taste-buds,  are  very 
numerous  in  the  fungi  form  and  circumvallate  papillae  of 
most  mammals,  but  in  the  cat  they  are  few  and  not  well 
differentiated.  These  tastebuds  occur  in  many  parts  of  the 
mucous. membrane  of  the  mouth  cavity,  each  being  supplied 
with  a  branch  of  the  glossopharyngeal  nerve. 

The  Visual  Organ. — The  special  organ  of  sight  is  the 
eye,  which  occupies  the  orbital  cavity  of  the  skull.  The  ball 
of  the  eye  is  protected  above  and  below  by  extensions  of 
skin  called  the  eyelids  or  palpebrae,  which  are  lined  with 
mucous  membrane,  a  transparent  layer  of  which,  known  as 
the  conjunctiva,  extends  over  the  front  of  the  eyeball  be- 
tween the  two  lids.  The  dorsal  lid  is  raised  by  the  levator 
palpebrae  muscle,  which  has  its  origin  in  the  occipitofrontalis 
muscle.  A  sphincter  muscle,  the  orbicularis  palpebrarum, 
lies  on  the  margin  of  the  lids,  and  by  its  contraction  closes 
the  eye. 


THE   NERVOUS    SYSTEM.  221 

The  point  on  either  side  where  the  two  eyelids  meet  is 
termed  the  canthus  or  angle.  At  the  medial  or  inner  canthus 
are  two  minute  apertures,  the  puncta  lachrymalia,  leading 
into  two  short  canals  which  unite  to  form  the  nasal  duct. 
The  lachrymal  canal,  which  forms  the  channel  for  this  duct, 
is  clearly  visible  in  the  lachrymal  bone  of  the  dried  skull. 
At  the  medial  canthus  there  is  a  prominent  fold  of  mucous 
membrane,  the  membrana  nictitans,  or  plica  semllunaris, 
which  is  a  rudimentary  structure  in  the  cat,  but  is  found 
well  developed  in  birds,  which  have  the  power  of  sweeping 
it  rapidly  across  the  eyeball,  thereby  removing  dust. 

On  the  inner  surface  of  each  lid  are  the  Meibomian 
glands.  The  lachrymal  gland  lies  in  the  dorso-lateral 
region  of  the  orbit,  and  its  ducts  open  on  the  ventral  sur- 
face of  the  upper  lid,  whence  the  tears  flow  over  the  con- 
junctiva ventrad  to  the  puncta  lachrymalia.  The  Harderian 
gland  is  the  very  small  gland  at  the  medial  canthus. 

The  muscles  controlling  the  movements  of  the  eyeball 
are  seven  in  number :  four  are  recti  muscles,  two  are  oblique, 
and  one  is  a  retractor.  The  recti  muscles  (Fig.  93)  origi- 
nate on  the  bone  around  the  optic  foramen,  and  are  inserted 
on  the  sclerotic  coat,  caudad  of  the  equatorial  ring.  The 
external  rectus  is  inserted  on  the  lateral  aspect ;  the  internal 
rectus,  on  the  medial  aspect;  the  superior  rectus,  on  the 
dorsal  aspect ;  and  the  inferior  rectus  on  the  ventral  aspect. 
The  superior  oblique  muscle  arises  from  the  sphenoid  bone 
medial  of  the  optic  foramen,  extends  along  the  medial  wall 
of  the  orbital  cavity  to  its  dorso-medial  margin,  where  it 
passes  through  a  tendinous  loop  fastened  to  the  frontal  bone 
and  then  turns  laterad  to  its  insertion  in  the  sclerotic  beneath 
the  superior  rectus.  The  inferior  oblique  arises  from  the 
lachrymal  bone  and  is  inserted  on  the  sclerotic  between  the 
external  and  inferior  recti  muscles.  The  above  muscles 
may  be  demonstrated  by  cutting  away  the  lateral  and  dorsal 


222 


ELEMENTS    OF   MAMMALIAN   ANATOMY. 


walls  of  the  orbital  cavity.  The  retractor  oculi  originates 
on  the  boundary  of  the  optic  foramen  and  is  inserted  into 
the  sclerotic  around  the  entrance  of  the  optic  nerve.  This 
muscle  is  completely  hidden  by  the  recti  muscles. 

The  eyeball  is  composed  of  three  membranes  and  three 
humors.  The  outer  coat,  the  sclerotic,  consists  of  the 
opaque  portion  forming  the  caudal  two-thirds,  and  the 
transparent  portion,  or  cornea,  forming  the  remainder  (Fig. 
no).  The  optic  nerve  pierces  the  sclerotic  a  little  mediad 
of  the  longitudinal  axis  of  the  eye.  The  surface  of  the 
cornea  is  more  strongly  curved  than  that  of  the  opaque  por- 


FIG.  no.     LONGITUDINAL  SECTION  OF  THE  EYE. 

aq,  Aqueous  humor ;  c,  cornea ;  cp,  capsule  of  the  lens ;  ch,  choroid ;  ci, 
ciliary  process ;  *,  iris ;  Ig,  ligament  of  lens ;  m,  ciliary  muscle ;  opn, 
optic  nerve :  rt,  retina ;  sc,  sclerotic  coat ;  os,  ora  serrata. 

tion  of  the  sclerotic,  and  contains  no  blood-vessels.  The 
second  or  middle  coat  of  the  eye  is  formed  by  the  choroid 
membrane  and  its  extension,  the  iris.  This  coat  is  incom- 
plete, as  there  is  an  aperture,  the  pupil,  through  the  iris  for 
the  admission  of  light.  The  choroid  appears  as  a  jet-black 
membrane,  less  than  half  as  thick  as  the  sclerotic,  lying 
closely  appressed  to  the  latter.  The  choroid  is  lined  in- 


THE   NERVOUS    SYSTEM.  223 

ternally  by  dark  pigment  cells,  except  in  the  caudal  area 
around  the  optic  nerve,  which  has  a  metallic  luster.  This 
portion  is  called  the  tapetum.  It  causes  the  shining  ap- 
pearance of  the  cat's  eyes  in  the  dark.  The  choroid  is  a 
vascular  membrane,  being  supplied  by  the  ophthalmic  artery, 
a  branch  of  the  internal  carotid. 

The  iris  is  attached  by  its  peripheral  margin  to  the 
sclerotic  and  choroid  coats,  and  hangs  free  in  the  aqueous 
humor.  It  gives  color  to  the  eye.  In  the  cat  it  is  yellowish, 
while  in  man  it  is  frequently  blue  or  black.  The  iris  is 
merely  a  curtain  to  regulate  the  amount  of  light  admitted 
to  the  retina.  There  is  a  sphincter  muscle  lying  in  it,  which 
by  contraction  renders  the  pupil  very  small.  There  is  prob- 
ably no  dilating  muscle  of  the  iris  present  in  the  cat.  The 
short,  thickened,  radial  projecting  folds  of  the  choroid  are 
the  ciliary  processes,  which  contain  numerous  blood-vessels, 
and  in  some  mammals  a  gland.  The  ciliary  muscle  arises 
from  the  sclerotic  coat  near  its  junction  with  the  cornea, 
and  is  inserted  into  the  cranial  part  of  the  choroid  coat. 

The  inner  membrane  of  the  eye  is  the  retina,  which  is  of 
a  light  gray  color  in  a  fresh  specimen  and  seems  quite  free 
from  the  choroid.  It  is  thickest  in  the  caudal  two-thirds 
of  the  cavity  of  the  eyeball  (Fig.  no).  At  the  base  of  the 
ciliary  bodies  it  seems  to  end  with  a  free  margin,  called  the 
ora  serrata.  In  reality  it  becomes  very  thin  here  and  is 
prolonged  over  the  ciliary  bodies  and  covers  the  caudal 
aspect  of  the  iris.  The  blind  spot  is  the  point  of  entrance 
of  the  optic  nerve,  laterad  of  which  is  the  yellow  spot,  or 
macula  lutea,  containing  the  fovea  centralis,  or  acute  point 
of  vision.  This  is  the  point  on  which  the  rays  of  light  are 
focused  when  the  cat  sees  distinctly. 

The  three  humors  of  the  eye  are  the  aqueous ',  the  crystal- 
line lens,  and  the  vitreous  humor.  The  aqueous  humor  is  a 
watery  fluid  occupying  the  cavity  between  the  cornea  and 


224  ELEMENTS   OF   MAMMALIAN   ANATOMY. 

crystalline  lens.  It  always  escapes  as  soon  as  the  cornea 
is  punctured.  The  vitreous  humor  is  of  a  jelly-like  con- 
sistency, filling  the  part  of  the  eyeball  caudad  of  the  lens. 
It  is  perfectly  transparent  and  is  surrounded  by  a  delicate 
capsule,  the  hyaline  membrane. 

The  crystalline  lens  is  a  transparent  biconvex  tissue  hav- 
ing a  vertical  diameter  of  about  one  centimeter  and  a  shorter 
diameter  through  its  optical  axis.  It  is  enclosed  in  a  trans- 
parent elastic  capsule,  some  of  whose  fibers  are  continued 
peripherad  as  the  suspensory  ligament  which  is  inserted  in 
the  choroid  coat  (Fig.  no). 

The  Auditory  Organ. — The  organ  of  hearing  is  com- 
posed of  three  parts — the  external  ear,  middle  ear,  and 
internal  ear.  The  first  consists  of  the  pinna  and  the  audi- 
torius  meatus  externus.  The  pinna  is  the  projecting  por- 
tion of  the  ear  capable  of  being  moved  by  muscles,  and  is 
composed  of  integument  strengthened  by  fibrocartilage. 
The  audit onus  meatus  externus  extends  from  the  base  of 
the  pinna  to  the  tympanic  membrane  (Fig.  1 1 1 ) .  Its  outer 
or  lateral  third  is  formed  by  cartilage,  and  the  remainder  by 
the  tympanic  portion  of  the  temporal  bone  (Fig.  17).  The 
meatus  is  lined  with  mucous  membrane  in  which  are  numer- 
ous sebaceous  and  oleaginous  glands.  The  latter  secrete 
the  wax  of  the  ear. 

The  middle  ear,  or  tympanum,,  is  an  irregular  cavity  about 
one  centimeter  in  diameter  contained  in  the  lateral  chamber 
of  the  bulla  (Fig.  in).  It  is  separated  from  the  external 
auditory  meatus  by  the  delicate  translucent  membrane,  the 
membrana  tympani.  The  petrous  bone  containing  the  in- 
ternal ear  forms  part  of  the  inner  or  medial  wall.  In  the 
petrous  bone  are  two  foramina  which  may  be  seen  in  a  dry 
skull  by  looking  through  the  external  auditory  meatus. 
The  more  dorsal  foramen  is  the  fenestra  ovalis,  which  in 
the  recent  state  is  closed  by  a  membrane  to  which  the  foot 


THE   NERVOUS    SYSTEM. 


225 


of  the  stapes  is  attached.  The  ventral  one  is  the  fenestra 
rotunduni,  also  closed  by  a  membrane  in  the  recent  state. 
In  the  dry  skull  the  fenestra  ovalis  opens  into  the  first  or 
basal  whorl  of  the  cochlea,  and  the  fenestra  rotundum  opens 
into  the  vestibule  of  the  internal  ear.  The  Eustachian  tube 
(Fig.  18),  whose  opening  may  be  seen  craniad  of  the  audi- 
tory bulla,  connects  the  middle  ear  with  the  posterior  nares 
and  thus  admits  air  to  the  tympanic  cavity. 

To  demonstrate  further  the  anatomy  of  the  middle  ear, 
one  should  clean  the  flesh  from  a 
fresh  or  preserved  head  and  care- 
fully cut  away  the  ventral  walls 
of  both  chambers  of  the  auditory 
bulla  (Fig.  17). 

In  the  middle,  ear  are  three 
bones,  the  malleus,  incus,  and 
stapes,  commonly  called  hammer, 
anvil,  and  stirrup.  They  form  a 
crooked  chain  across  the  cavity. 
The  long  process  of  the  malleus  is 
fastened  throughout  nearly  its 
whole  length  to  the  inner  surface 
of  the  membrana  tympani,  and  its 
enlarged  extremity  articulates 
with  the  body  of  the  incus.  The 
latter  has  two  legs,  to  one  of 
which  the  stapes  is  attached.  The 
base  of  the  stapes  is  inserted  in 
the  membrane  closing  the  fenestra  ovalis  (Figs.  17  and 

no. 

The  internal  ear,  or  labyrinth,  consists  of  three  parts — 
the  vestibule,  cochlea,  and  semicircular  canals  (Figs.  18 
and  in).  All  of  these  parts  are  of  membrane  and  lie  in 
cavities  of  corresponding  shape  within  the  petrous  bone. 


FIG.  in.  DIAGRAM  OF  THE 
MAMMALIAN  EAR. 

The  internal  ear  is  repre- 
sented removed  about  a 
centimeter  from  the  mid- 
dle ear  and  slightly  ro- 
tated to  the  left.  The 
base  of  the  stapes,  s,  in 
nature,  covers  the  fenes- 
tra ovalis,  ov,  c,  basal 
whorl  of  the  cochlea ;  ea, 
external  auditory  meatus ; 
eu,  opening  of  the  Eu- 
stachian tube ;  i,  incus ;  in, 
malleus;  sc,  semicircular 
canals;  ve,  vestibule;  t, 
tympanum. 


226  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

A  lymphoid  fluid,  the  perilymph,  floats  the  delicate  mem- 
branous internal  ear  within  its  bony  cavity,  while  within 
the  membrane  is  a  similar  fluid,  the  endolymph.  The  vesti- 
bule is  a  small  sac  adjacent  to  the  tympanum,  and  may  be 
seen  by  looking  through  the  fenestra  ovalis.  From  the 
dorso-caudal  aspect  of  the  vestibule,  arch  three  semicircular 
cunals  at  nearly  right  angles  to  one  another.  The  external 
semicircular  canal  is  in  a  horizontal  plane  and  surrounds  a 
small  fossa  almost  caudad  of  the  fenestra  ovalis.  The 
superior  semicircular  canal  lies  in  a  transverse  plane  caudad 


FIG.    112.     SECTION   OF  THE   COCHLEA   OF  THE   CALF.       X  10. — (From 
Ellenberger,  after  Kolliker.} 

a,  Modiolus ;  c,  scala  tympani ;  v,  scala  vestibuli ;  Im,  lamina  spiralis ;  pt, 
portion  of  the  petrous  bone ;  r,  scala  media,  or  ductus  cochlearis. 

to  the  preceding.  The  posterior  semicircular  canal  lies  in  a 
vertical  longitudinal  plane,  immediately  laterad  from  the 
jugular  foramen. 

The  cochlea  is  a  coiled  canal  lying  within  the  coiled 
cavity,  the  bony  cochlea,  extending  craniad  from  the  vesti- 
bule. If  both  chambers  of  the  auditory  bulla  are  removed 
and  a  bristle  thrust  into  the  fenestra  rotundum  (Fig.  17), 
it  will  enter  the  basal  whorl  of  the  bony  cochlea.  A  line 
drawn  from  the  lateral  margin  of  the  foramen  ovale  to  the 


THE   NERVOUS    SYSTEM.  227 

medial  margin  of  the  fenestra  rotundum  passes  through  the 
apex  and  middle  of  the  base  of  the  cochlea,  which  may  be 
rendered  visible  by  carefully  clipping  off  with  the  bone- 
forceps  the  ventral  portion  of  the  petrous  bone  along  the 
line  indicated.  This  coiled  canal,  the  cochlea,  is  divided 
into  two  channels  by  a  shelf  of  bone,  the  lamina  spiralis, 
projecting  from  the  central  axis  or  modiolus  of  the  coil 
(Fig.  112).  The  bony  lamina  extends  but  partly  across  the 
canal,  the  remaining  distance  being  bridged  by  membrane. 
The  cranial  channel,  or  the  one  nearer  the  apex  of  the 
cochlea,  is  called  the  scala  vestibuli.  The  other  is  the  scala 
tympani. 

The  semicircular  canals  probably  have  nothing  to  do  with 
hearing,  as  they  are  well  developed  in  fishes,  some  of  which 
do  not  hear  at  all.  They  may  aid  in  helping  the  cat  to  main- 
tain its  equilibrium.  The  auditory  nerve,  however,  is  dis- 
tributed to  the  vestibule  and  semicircular  canals  as  well  as 
to  the  cochlea  upon  the  lamina  spiralis,  where  the  organ  of 
Corti,  the  essential  organ  of  hearing,  is  located. 


REMARKS  ON  THE  MAMMALIAN  NERVOUS  SYSTEM. 

So  far  as  known,  the  relation  of  the  sympathetic  to  the 
peripheral  and  central  nervous  systems  is  the  same  in  all 
mammals.  The  number  of  spinal  nerves  varies  with  the 
number  of  vertebrae.  The  distribution  of  these  nerves, 
however,  is  approximately  the  same  in  all  forms  with  five 
digits.  In  those  having  a  less  number  of  digits  the  nerve 
branch  corresponding  to  the  lacking  digit  or  digits  is  want- 
ing. The  arrangement  of  the  columns  or  tracts  of  fibers  in 
the  spinal  cord  is  very  similar  in  all  the  orders.  The  anterior 
or  direct  pyramidal  tract,  however,  is  partially  or  wholly 
absent  in  most  orders  below  the  Primates.  It  is  best  devel- 


228  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

oped  in  man,  although  in  a  number  of  cases  it  has  been  found 
entirely  wanting  in  the  human.     The  number  of  the  cranial 


FIG.  113.     PHOTOGRAPH  OF  THE  HUMAN  BRAIN  FROM  THE  LATERAL 
ASPECT.     Two  fifths  natural  size. 

nerves  is  always  twelve  and  their  distribution  is  very  similar 
in  all  forms  investigated. 

The  structure  of  the  brain  in  the  Ornithodelphia  and 
Didelphia  differs  considerably  from  that  of  the  Mono- 
delphia.  In  the  two  former  subclasses  the  corpus  callosum 
and  fornix  are  very  rudimentary,  but  the  anterior  commis- 
sure piercing  the  corpora  striata  is  unusually  large.  The 
fibers,  which  in  the  Monodelphia  arise  from  the  cells  of  the 
hippocampus,  and  extend  craniad  to  form  the  fornix,  cross 
transversely  to  the  opposite  hippocampus  in  the  two  lower 
subclasses. 

In  all  higher  mammals  the  cerebrum  is  greatly  convoluted, 
but  in  the  lower  ones  the  convolutions  are  few  or  almost 
absent,  as  in  Ornithorhynchus.  The  above-mentioned 
features  show  that  the  ornithodelphian  brain  presents  a 


THE   NERVOUS    SYSTEM. 


229 


FIG.  114.  BRAIN  OF  THE 
RABBIT  FROM  DORSAL 
ASPECT. 

c,  cerebellum.  Three 
fifths  natural  size. 


striking  similarity  to  the  brains  of 
reptiles  and  birds.  The  brains  of 
Rodentia  possess  but  few  convo- 
lutions, while  the  brain  of  man  is 
the  most  highly  convoluted. 

The  size  of  the  brain  varies 
widely.  As  a  rule,  the  larger  the 
brain  in  proportion  to  the  size  of  the 
animal,  the  greater  is  its  intelligence. 
However,  in  man  this  statement 
does  not  always  hold  true,  as  an  indi- 
vidual with  a  small  brain  may  be 
much  more  capable  mentally  than 
one  with  a  large  brain.  Mental 
power  in  man  seems  to  depend  upon 
the  development  of  the  cells  and 
fibers  of  the  brain. 

The  average  weight  of  a  male  human  brain  is  about  three 
pounds;  of  a  female,  about  two  and  two-thirds  pounds. 
The  human  brain  is  -^  the  weight  of  the  body;  the  ape's, 
2*9;  the  rat's,  ¥^;  the  sheep's,  g|T;  and  the  elephant's,  -g^-0 . 
The  brain  of  man  is  larger  than  that  of  any  other  mammal 
except  the  whale  and  elephant.  The  brain  of  a  large  whale 
weighs  over  four  pounds,  while  that  of  a  large  elephant 
will  weigh  about  ten  pounds. 

PRACTICAL   QUESTIONS    AND    SUGGESTIONS. 

1.  How  many  nerves  transmit  the  stimuli  received  by  the  organs  of 
special  sense? 

2.  Where  are  the  sense  organs  of  pain  located? 

3.  How  many  sense  organs  are  visible  in  the  mesentery  of  your 
specimen? 

4.  Describe  the  path  of  a  stimulus  from  the  index  finger  to  the  brain. 

5.  Through  which  nerve  roots  would  the  stimuli  received  by  the 
cutaneous  sense  organs  pass  into  the  cord? 

6.  Describe  the  nerves  transmitting  the  stimuli  from  the  olfactory 
organ. 


230  ELEMENTS    OF   MAMMALIAN   ANATOMY. 

7.  Describe  the  gland  secreting  the  tears  and  how  they  reach  the 
nasal  cavity. 

8.  By  cutting  away  the  lateral  and  dorsal  walls  of  the  orbit  dissect 
the  muscles  of  the  eyeball  and  make  a  drawing  of  them,  labelling  all 
parts. 

9.  What  nerves  control  the  movements  of  the  eyeball? 

10.  Procure  the   eyes   of   any  mammal    from  the   butcher-shop   or 
slaughterhouse ;  bisect  one  in  the  meridional  and  the  other  in  the  equa- 
torial direction.     Make  a  drawing  of  the  features  seen  and  label. 

11.  Remove  the  crystalline  lens  from  a  fresh  eye,  describe  its  size, 
shape,  structure,  length  of  focus,  and  power  of  magnification. 

12.  Describe  the  path  of  a  stimulus  from  the  retina  to  the  area  of 
sight  in  the  brain. 

13.  Name  every  feature  visible  in  the  eyes  you  have  dissected. 

14.  What  nerve  supplies  the  auditory  organ? 

15.  Describe  the  middle  ear. 

16.  In  what  part  of  the  temporal  bone  is  the  internal  ear  located? 

17.  By  looking  into  the  auditorius  meatus  of  the  dried  skull  two  open- 
ings are  seen.     Into  which  portions  of  the  internal  ear  do  these  lead? 

18.  Write  a  description  of  the  internal  ear. 

19.  Mention  some  important  points  of  difference  in  the  nervous  sys- 
tem of  various  mammals. 

20.  What  relation,  if  any,  between  intellectual  ability  and  brain  de- 
velopment? 


GLOSSARY. 


Ab  du' cens  (ab,  from;  ducens,  leading)  :  the  sixth  cranial  nerve. 

Ab  due' tor  (ab,  from;  duco,  I  lead)  :  a  muscle  drawing  a  part  outward. 

Ac  e  tab' u  him  (small  cup)  :  cavity  of  the  innominate  bone  for  articu- 
lation with  the  femur. 

Aero' mi  on  (summit  of  shoulder):  name  of  certain  parts  at  the 
shoulder. 

Ad :  a  Latin  prefix  of  words ;  signifying  to,  toward  or  at. 

Ad  due'  tor  (ad,  to ;  duco,  I  draw)  :  a  muscle  drawing  a  part  inward. 

Afferent  (ad,  to;  fero,  I  carry)  :  the  name  of  a  nerve  carrying  an 
impulse  to  the  brain  or  cord,  and  also  applied  to  a  vessel  conveying 
fluid  to  the  organ  in  which  a  physiologic  process  is  to  occur. 

An  aes  thet'  ic  (want  of  feeling)  :  any  drug  which  when  used  exter- 
nally or  internally  causes  loss  of  feeling. 

Alisphen'oid  (a/a,  wing;  sphen,  wedge;  old,  like):  the  wing-like 
part  of  the  sphenoid  bone. 

Al  ve'  o  lar  (alveolus,  small  hollow)  :  relating  to  the  sockets  of  the 
teeth. 

Al  ve'  o  lus  :  the  socket  of  a  tooth. 

Am  phi  ar  thro' sis  (amphi,  around;  arthron,  a  joint)  :  a  joint  in  which 
there  is  limited  movement  in  every  direction. 

Amphib'ians  (amphi,  both;  bios,  life)  :  a  class  of  vertebrates  includ- 
ing frogs  which  spend  part  of  the  life  in  water  and  part  on  land. 

A  nas  to  mo'  sis :  the  intercommunication  of  vessels. 

An  chy  lo' sis  (stiff  joint)  :  a  firm  union  of  the  bones  forming  a  joint. 

An'nular  (annulus,  a  ring)  :  a  name  given  to  the  encircling  ligaments 
at  the  wrist  and  ankle. 

Ap  o  neu  ro'  sis  (apo,  from ;  neuron,  a  tendon)  :  a  membranous  expan- 
sion of  a  tendon. 

A  rach'  noid  (like  a  spider's  web)  :  the  delicate  middle  membrane  en- 
veloping the  brain  and  spinal  cord. 

A  re' o  lar  (open  space)  :  relating  to  connective  tissue  loosely  woven. 

Ar  ti  o  dac' ty  la  (even-fingered)  :  those  ungulates  having  an  even  num- 
ber of  digits  on  each  foot. 

Aryt'enoid  (arutaina,  pitcher;  old,  like)  :  the  name  of  a  pair  of  car- 
tilages of  the  larynx. 

Auric'ular  (auricula,  outer  ear)  :  relating  to  the  ear. 

Au'  dit  o  ry  (audire,  to  hear)  :  pertaining  to  the  act  or  the  organs  of 
hearing. 

231 


223  GLOSSARY. 

Axil' la  (axilla,  armpit). 

Ax'  il  la  ry :  a  name  given  to  several  structures  in  the  region  of  the 

armpit. 
Ax'  one :  the  process  which  carries  the  impulse  away  from  a  nerve  cell. 

Bi' ceps   (bis,  twice;  caput,  head):  a  term  applied  to  muscles  having 

two  origins. 

Brach  (brachium,  arm). 

Brach'  i  al :  a  name  given  to  several  structures  in  the  upper  arm  region. 
Bron'  chi :  plural  of  bronchus. 
Bron'  chus  (brogkos,  windpipe)  :  the  two  tubes  into  which  the  trachea 

divides. 
Buc'  cal  (bucca,  cheek)  :  pertaining  to  the  cheek. 

Cae'  cum  (blind)  :  first  part  of  large  intestine. 

Cal  ca'  ne  um  (calcaneum,  the  heel)  :  the  os  calcis  or  heel-bone. 

Cal  lo' sum   (callosus,  thick-skinned):   the  largest  commissure  of  the 

brain. 

Can  a  lie'  u  li :  the  small  canals  opening  into  the  lacunae  of  bone. 
Can'nula  (canna,  a  tube)  :  a  small  tube. 
Capit'ulum  (capitulum,  a  small  head)  :  the  enlarged  terminal  portion 

of  an  organ. 

Car'  di  ac  (kardia,  the  heart)  :  pertaining  to  the  heart. 
Ca  rot'  id :  the  chief  artery  lying  on  either  side  of  the  windpipe. 
Car' pal  (karpos,  wrist)  :  pertaining  to  the  wrist. 
Cau'  dad :  toward  the  tail. 
Cau'  dal  (cauda,  tail)  :  relating  to  the  tail. 
Cen'  trum :  the  body  of  a  vertebra. 
Ceph'alic  (kephala,  head)  :  relating  to  the  head. 
Cer  a  to  hy'  al :  a  part  of  the  hyoid  apparatus. 
Cer'vical  (cervix,  neck)  :  a  name  applied  to  structures  in  the  region 

of  the  neck. 

Cer'  vi  dae :  the  name  of  the  deer  family. 
Chev'  ron  bones :  the  bones  on  the  underside  of  some  of  the  caudal 

vertebrae. 

Chi' asm  (kir  azm,  mark  crosswise)  :  the  optic  commissure. 
Chi  rop' te  ra   (cheir,  hand;  pteron,  wing)  :  an  order  of  mammals  in- 
cluding the  bats. 
Cho  an'  as  :  the  posterior  nares. 
Cho'  roid :  the  middle  lining  of  the  eyeball. 
Cir  cum  val'  late   (circumvallere,  to  surround  with  a  wall):  the  name 

of  the  large  papillae  at  the  base  of  the  tongue. 
Clit'  or  is :  a  small  erectile  organ  occupying  the  same  relative  position 

in  the  female  as  the  penis  occupies  in  the  male. 
Coc' cyx  (kokkux,  the  cuckoo,  resembling  the  bill)  :  the  several  united 

vertebrae  forming  the  tail  in  man. 


GLOSSARY.  233 

Coch'lea  (kokf  le  ah)  (kochlos,  a  conch-shell)  :  the  coiled  canal  of  the 

internal  ear. 
Cce'liac   (ser  le  ak)    (koilia,  belly):  a  name  applied  to  a  large  artery 

and  a  nerve  plexus  in  the  abdomen. 
Cce'  lorn  (ser  lum)  :  the  body  cavity. 
Con'  dyle  (kondulos,  a  knuckle)  :  a  paired  rounded  eminence  of  a  bone 

for  articulation. 

Cor'  nu  (a  horn)  :  a  name  given  certain  structures  resembling  a  horn. 
Cor'  nu  a :  the  plural  of  cornu. 
Cor'onoid  (corona,  crown;  old,  like). 
Cor'  por  a    (corpus,  body):   a  name  given  to  certain  parts  having  a 

rounded  or  ovoid  shape. 
Cor'  pus :  singular  of  corpora. 
Cos'  ta  (costa,  rib). 
Cos'  tal :  pertaining  to  the  ribs. 
Cot' yl  old   (kotula,  a  cup;  old,  like):  relating  to  the  articular  cavity 

in  the  innominate  bone. 
Cra'  ni  ad :  toward  the  plane  in  front  of  the  cranium  and  perpendicular 

to  the  spinal  axis. 

Cra'  ni  al :  pertaining  to  the  cranium. 
Cra'nium:  those  bones  of  the  skull  encasing  the  brain. 
Cru'  ra :  plural  of  crus. 
Crus  (crus,  a  leg)-:  the  part  of  the  leg  between  the  knee  and  ankle.     It 

is  also  applied  to  structures  resembling  the  leg. 
Cu'  bold  (like  a  cube)  :  one  of  the  tarsal  bones. 
Cunea'tus  (kuneus,  a  wedge)  :  a  fiber  tract  in  the  spinal  cord. 
Cune'iform  (wedge-shaped)  :  bones  of  the  ankle  and  wrist. 
Cuta'neous  (cutis,  the  skin)  :  relating  to  the  skin. 

De  cus  sa'  tion  (decussatus,  crossed)  :  an  oblique  crossing  of  the  nerves. 

Demifac'et  (demi,  half;  facette,  little  face)  :  the  articular  surface  on 
the  body  of  a  vertebra  for  the  articulation  of  half  the  head  of  a  rib. 

Den'  drites  (dendron,  a  tree)  :  the  processes  of  a  nerve  cell  which 
transmit  the  impulse  toward  the  cell-body. 

Di  aph'  y  sis  (dia,  between ;  phuein,  to  grow)  :  the  shaft  of  a  long  bone. 

Diaste'ma  (diastema,  a  distance)  :  a  space  between  any  two  consecu- 
tive teeth. 

Di  ar  thro'  sis  (dia,  throughout ;  arthrosis,  articulation)  :  a  form  of 
articulation  giving  much  freedom  of  motion. 

Di  del' phi  a  (dis,  twice;  delphus,  uterus):  an  order  of  mammals  in- 
cluding the  kangaroos  and  opossums  in  which  a  paired  uterus  is 
present. 

Di  en  ceph' a  Ion  (dia,  between;  egkephalos,  the  brain):  the  tween 
brain  formed  largely  by  the  optic  thalami. 

Di  gas'  trie  (dis,  double ;  gaster,  belly)  :  the  muscle  depressing  the 
lower  jaw. 


234  GLOSSARY. 

Dig'  it  (digitus,  a  finger)  :  the  name  of  a  finger  or  toe. 

Dig  it  or'  um :  of  digits. 

Diph'yodont  (diphus,  twofold;  odous,  tooth)  :  mammals  having  two 

sets  of  teeth. 

Dis'  tad :  away  from  the  axis  of  the  body. 
Dis'  tal :  the  part  farther  from  the  axis  of  the  body. 
Dor'  sad   (dorsum,  the  back)  :  toward  the  line  passing  from  head  to 

tail  along  the  tips  of  the  spinous  processes. 
Duode'num  (duodeni,  twelve  each)  :  first  part  of  the  small  intestine; 

in  man  it  is  twelve  finger-breadths. 
Du  ra  ma'  ter   (durus,  hard ;  mater,  mother)  :  the  outer  membrane  of 

the  brain  and  cord. 

E  den  ta' ta  (e,  without;  dens,  a  tooth):  an  order  of  mammals  some 
of  which  have  no  teeth. 

Efferent  (efferens,  carrying  from)  :  the  opposite  of  afferent. 

Em'  bry  o :  the  undeveloped  young. 

Enceph'alon  (en,  in;  kephala,  the  head)  :  the  brain. 

Endomys'ium  (endon,  within;  mus,  muscle):  the  extension  of  the 
perimysium  between  the  muscular  fibers. 

En' si  form  (ensis,  sword;  forma,  form):  the  cartilaginous  process  at 
the  caudal  end  of  the  sternum. 

Ep  i  did' y  mis  (epi,  upon;  didumoi,  the  testes)  :  the  contorted  tubule 
forming  the  small  body  lying  against  the  testis. 

Ep  i  mys' i  um  (epi,  upon;  mus,  muscle)  :  the  delicate  membrane  envel- 
oping muscle. 

Epiph'yses  (epi,  upon;  phuein,  to  grow)  :  a  process  of  bone  attached 
for  a  time  to  another  bone  by  cartilage,  but  later  becoming  firmly 
united  to  it. 

Ep  i  the'  li  um :  the  outer  layer  of  the  skin  and  all  mucous  surface. 

Eth'  moid  (ethmos,  a  sieve;  old,  like)  :  the  bone  at  the  root  of  the  nose. 

Eusta'chian  (u  sta'  ke  an}    (named  after  the  anatomist  Eustachio). 

Euthe'ria  (eus,  good;  therion,  beast)  :  a  subclass  including  all  mam- 
mals above  the  marsupials. 

Fac'  et  (facette,  a  little  face)  :  a  small  plane  surface  usually  on  a  bone 

for  articulation. 
Fal  lo'  pi  an  tube :  the  canal  conducting  the  eggs  from  the  ovary  to  the 

uterus. 

Fal  lo'  pi  us :  a  noted  Italian  anatomist. 

Fas'  ci  a   (fash'  e  ah)  :  the  membranous  fibrous  covering  of  muscles. 
Fas  cic'  u  lus  (fascis,  a  bundle)  :  a  little  bundle  of  fibers  forming  part 

of  a  nerve  or  muscle. 
Fau'  ces  (fawr  sez}  :  that  part  of  the  throat  surrounded  by  the  palate, 

tonsils  and  uvula. 


GLOSSARY.  235 

Penes' tra  (a  window). 

Fil'iform  (filum,  thread;  forma,  form)  :  name  of  papillae  on  tongue. 

Fo  ra'  men  (forare,  to  pierce)  :  a  passage  or  opening,  usually  in  bone, 
for  the  transmission  of  nerves  or  vessels. 

Fo  ram'  i  na :  the  plural  of  foramen. 

For  mal'  de  hyde  :  an  excellent  disinfectant. 

For'  mal  in :  a  40  per  cent,  solution  of  formaldehyde  in  water. 

For'  nix  (an  arch)  :  the  projecting  bundle  of  fibers  from  the  gyrus  hip- 
pocampus, beneath  the  corpus  callosum. 

Fos'  sa  (a  ditch)  :  a  depression  or  furrow. 

Funic'ulus  (funis,  a  cord)  :  applied  to  various  cord-like  structures. 

Gas'  trie  (gaster,  stomach)  :  relating  to  the  stomach. 

Gas  troc  ne' mi  us  (gaster,  stomach;  knema,  leg)  :  large  muscle  in  the 
calf  of  the  leg. 

Gen'  e  ra  :  plural  of  genus. 

Ge  nic  u  la'  turn  (geniculare,  to  bend  the  knee)  :  a  name  applied  to  cer- 
tain bodies  in  the  brain. 

Gen'  us :  a  species  or  collection  of  species  marked  by  one  or  more  com- 
mon characteristics  distinguishing  them  from  other  groups. 

Ging'lymus  (gigglumos,  a  hinge)  :  a  kind  of  joint  having  free  motion 
in  two  directions. 

Glen' oid  (glena,  a  cavity;  old,  like)  :  pertaining  to  a  shallow  cavity. 

Glos'  sa :  the  tongue. 

Glu'  te  al :  pertaining  to  the  buttocks. 

Glu'  te  us  (gloutos,  buttock). 

Gly'  co  gen  (glukos,  sweet)  :  animal  starch. 

Grac'ilis  (slender)  :  the  name  of  a  muscle  in  the  leg. 

Gy'  ri :  plural  of  gyrus. 

Gy'  rus  (guros,  a  circle)  :  a  convolution  of  the  brain. 

Hal'lucis  (from  hallux,  the  great  toe). 

He  pat'  ic  (hepar,  liver)  :  pertaining  to  the  liver. 

Het' er  o  dont    (heteros,  other;   odous,  tooth):   having  teeth  of  more 

than  one  kind. 
Horn'  o  dont  (homos,  the  same;  odous,  tooth)  :  having  teeth  all  of  one 

form. 

Hy'  oid :  the  name  of  the  bone  at  the  root  of  the  tongue. 
Hy'  po :  under. 

Hy  po  gas'  trie  :  under  the  stomach. 
Hy  po  glos'  sus  :   under  the  tongue. 

In'  fra :  below. 

In  fra  or'  bit  al :  under  the  orbit. 


GLOSSARY. 

II'  e  um  (eilo,  twist)  :  the  last  part  of  the  small  intestine. 

II'  i  ac   {ilia,  the  flanks)  :  pertaining  to  the  region  of  the  ilium  or  hip 

bone. 
In'  guin  al    (in'  gwin  al}  :    pertaining   to    the    groin   or   ventral    region 

where  the  pelvic  limb  joins  the  body. 
In'  ter :  a  Latin  prefix  meaning  between. 
In  ter  cos'  tal :  between  the  ribs. 
In  ter  os'  se  ous :  between  the  bones. 
In  ter  ver'  te  bral :  between  the  vertebrae. 
Is'chium  («V  kium~)  :  the  middle  part  of  the  innominate  bone. 

Je  jun'  um  (jejunus,  empty)  :  the  two  fifths  of  the  small  intestine  ex- 
tending between  the  duodenum  and  ileum. 
Ju'  gal  (jugum,  a  yoke)  :  the  malar  bone. 
Ju'  gu  lar  (fugulum,  throat)  :  the  name  of  the  large  veins  in  the  neck. 

Lac' er  um  (laceros,  torn)  :  name  of  foramina  in  the  skull. 

Lach'  ry  mal  (lachryma,  a  tear)  :  pertaining  to  the  lachrymal  apparatus. 

Lac' te  als    (lac,  milk):   the  lymphatics   of  the  small  intestine  which 

take  up  the  chyle  and  carry  it  to  the  thoracic  duct. 
Lamb  doi'  dal  (after  a  Greek  letter)  :  pertaining  to  the  suture  between 

the  parietal  and  occipital  bones. 

Lam'  i  na  (a  plate  or  scale)  :  a  term  designating  a  thin  layer  of  tissue. 
Lar'  ynx :  the  cartilaginous  tube  at  the  cranial  end  of  the  trachea. 
Lat' er  ad  (latus,  side;  ad,  to)  :  toward  one  side. 
Lat'  er  al :  pertaining  to  the  side. 

La  tis'  si  mus  (broadest)  :  a  name  applied  to  certain  muscles. 
Le  va'  tor  (a  lifter)  :  a  name  given  to  muscles  which  raise  parts. 
Lin'  gual  (lingua,  tongue)  :  pertaining  to  the  tongue. 
Lum'  bar  (lumbus,  the  loin)  :  relating  to  the  region  of  the  loins  which 

is  the  lower  part  of  the  back. 
Lymphat'ics  (lympha,  water)  :  the  absorbent  system. 

Mag'num  (great). 

Ma' lar  (mala,  cheek). 

Mal  le'  o  lus  (malleus,  hammer)  :  a  process  of  bone. 

Mal  pigh'  i :  an  Italian  anatomist. 

Mam  ma'  li  a  (mamma,  breast)  :  the  highest  class  of  vertebrates. 

Manu'brium  (a  handle)  :  the  cranial  piece  of  the  breastbone. 

Ma'  nus  (hand)  :  the  hand. 

Marsupia'lia  (marsupos,  a  pouch):  a  subclass  of  mammals  having 

a  pouch  beneath  the  belly  in  which  they  carry  the  young. 
Ma'  ter  (mother). 
Mas' toid   (mastos,  breast;  oid,  like):  the  process  of  bone  behind  the 

ear. 


GLOSSARY.  237 

Me  a' tus  (passage)  :  a  channel  or  canal. 

Me'  di  ad  (medius,  middle)  :  toward  the  middle. 

Me'  di  al :  pertaining  to  the  middle. 

Me  di  as  ti' num  (standing  in  the  middle)  :  the  space  between  the  lungs, 

including  the  heart  and  other  organs. 
Med' ul  la  ry  (medulla,  marrow)  :  pertaining  to  the  marrow  within  the 

bones. 
Men  in  ge'  al    (menigx,  membrane)  :   pertaining  to  the  membranes  of 

the  brain  or  cord. 

Men'  tal  (mentum,  chin)  :  pertaining  to  structures  about  the  chin. 
Mes  en  ter'  ic    (mesos,  middle ;   enter  on,  intestine)  :   pertaining  to  the 

mesentery. 
Mes' en  ter  y:  a  fold  of  the  peritoneum  joining  parts  of  the  intestine 

to  the  dorsal  part  of  the  abdominal  cavity. 
Met' a  (beyond). 
Mes  en  ceph' a  Ion  (mesos,  middle;  encephalon,  brain)  :  the  mid-brain, 

consisting  of  the  corpora  quadrigemina  and  crura  cerebri. 
Met  en  ceph'  a  Ion :  the  pons  Varolii  and  cerebellum. 
Mo  di'  o  lus :  the  central  pillar  or  axis  of  the  cochlea. 
Mon'ophydont    (monos,    single;    phuein,    to    grow;    odous,    tooth): 

having  only  one  set  of  teeth  during  life. 
Mon  o  tre'  ma  ta  (monos,  single ;  tremos,  hole)  :  the  lowest  subclass  of 

mammals.     The  intestinal  and  urinary  products  are  voided  through 

one  opening  as  in  birds ;  duck  bill  and  spiny  ant  eater. 
Morphol'ogy  (morpha,  form;  logos,  discourse)  :  that  part  of  biology 

dealing  specially  with  form  and  structure. 
My  el  en  ceph'  a  Ion  (myelos,  marrow  ;  encephalon,  brain)  :  the  medulla 

oblongata. 
Mo'  tor  (movere,  to  move)  :  a  name  given  nerves  stimulating  muscles. 

Neu'  ral  (neuron,  nerve)  :  pertaining  to  a  nerve. 
Neu'  rone :  a  nerve  cell  with  all  its  processes. 
Nu'  clei :  plural  of  nucleus. 

Nu' cle  us  (nux,  a  nut)  :  the  essential  part  of  every  cell;  also  applied 
to  a  definite  bunch  of  nerve  cells. 

Ob' tu  ra  tor :  the  name  of  the  large  foramen  in  the  innominate  bone 

or  of  structures  near  to  it. 
Occip'ital    (ob,  against;   caput,  the  head):    relating  to  structures  in 

the  region  of  the  back  part  of  the  head. 
Oc' u  lar  (oculus,  the  eye)  :  pertaining  to  the  eye. 
O  don' toid  (odous,  tooth;  old,  like)  :  relating  to  the  tooth-like  process 

of  the  axis. 

Oid:  a  common  suffix  derived  from  Greek  eidos  and  signifying  like. 
O  lee' ran  on  (olea,  elbow;  kranion,  head)  :  process  of  the  ulna. 


238  GLOSSARY. 

O  men/  turn :  a  fold  of  the  peritoneum  connecting  the  abdominal  viscera. 

Olfac'tory  (olfacere,  to  smell)  :  pertaining  to  the  nose. 

Oph  thai'  mic  (ophthalmos,  eye)  :  pertaining  to  the  eye. 

Op' tic  (optikos,  to  see)  :  relating  to  the  eye. 

O'  ra :  mouth. 

Or' bit  al  (orbis,  circle)  :  pertaining  to  the  cavity  for  the  eye. 

Or'  gan :  any  part  having  a  definite  function. 

Or  nith  o  del' phi  a     (ornis,    bird;     delphus,    womb):    the    oviparous 

mammals. 
Os:  bone. 

O'  va :  plural  of  ovum. 
O  va'  le  :  oval. 
O  vip'  a  rous  (ovum,  egg;  parere,  to  bring  forth)  :  those  animals  which 

deposit  eggs  instead  of  bringing  forth  living  young. 
O'  vum :  egg. 

Pa  ri'  e  tal  (paries,  a  wall). 

Par  ot'  id  (para,  near ;  ous,  ear)  :  the  name  of  a  salivary  gland. 

Pec'  to  ral  (pectus,  breast)  :  pertaining  to  structures  in  the  region  of 
the  breast. 

Ped'  i  cles  (pediculus,  a  little  foot)  :  the  foot  of  the  neural  arch. 

Pe'  dun  cles  (pedunculus,  a  little  foot)  :  bands  of  fibers  uniting  certain 
parts  of  the  brain. 

Pel'  vie :  relating  to  the  cavity  between  the  innominate  bones. 

Perimys'ium  (peri,  around;  mus,  a  muscle):  the  tissue  which  en- 
velops the  primary  bundles  of  muscle  fibers. 

Per  is  so  dac'  ty  la  (perissos,  odd ;  dactyl,  finger)  :  those  ungulates 
having  an  odd  number  of  digits. 

Pe  riph'  e  ral :  pertaining  to  the  outside. 

Peritone'um  (peri,  around;  teinein,  to  stretch):  the  serous  mem- 
brane lining  the  abdominal  cavity  and  surrounding  most  of  the 
organs  within  it. 

Per  o  ne'  al  (perone,  a  pin)  :  relating  to  the  fibula. 

Pe'  des  :  plural  of  pes. 

Pes:  foot. 

Pha  Ian'  ges :  plural  of  phalanx. 

Phal'  anx :  one  of  the  bones  of  the  fingers  or  toes. 

Phar'  ynx  (throat)  :  the  cavity  back  of  the  mouth. 

Phren'  ic  (phren,  diaphragm)  :  pertaining  to  the  diaphragm. 

Phy  log' e  ny  (phula,  tribe;  genas,  producing)  :  that  science  treating  of 
the  evolution  of  a  group. 

Pi'  a  ma'  ter  (soft  mother)  :  the  delicate  membrane  next  to  the  brain 
and  cord. 

Pneu  mo  gas' trie  (pneuma,  air;  gaster,  stomach)  :  the  vagus  nerve. 

Pons :  bridge. 


GLOSSARY.  239 

Poplit'eal    (poples,   knee):   pertaining  to  the  caudal    region   of   the 

knee-joint 

Post:  a  common  prefix  meaning  after  or  behind. 
Pri  ma'  tes   {primus,  first)  :  the  highest  order  of  mammals,  including 

man  and  the  monkeys. 

Pro  fun'  da  (profundus,  deep)  :  a  term  given  to  a  part  deep-seated. 
Pro  to  chor  da'  ta   (protos,  first;  chorda,  cord):  those  forms  between 

the  invertebrates  and  vertebrates.     Seasquirts. 

Pro  to  the' ri  a  (protos,  first;  therion,  beast)  :  the  oviparous  mammals. 
Prox'  i  mad :  toward  the  central  axis  of  the  body. 
Prox'  i  mal :  that  part  nearest  to  the  central  axis  of  the  body. 
Pter'ygoid  (pteron,  wing;  old,  like)  :  part  of  the  sphenoid  bone. 
Pul'  mo  na  ry  (pulmo,  lung)  :  pertaining  to  the  lung. 
Py  lor'  ic  (pyloros,  gate-keeper)  :  the  opening  of  the  stomach  into  the 

duodenum. 

Quad'riceps   (quadri,  four;  caput,  head). 
Quad  ri  gem'  i  na :  plural  of  quadrigeminum. 

Quad  ri  gem'  i  num  (quadri,  four ;  geminus,  twin  born)  :  part  of  the 
brain. 

Ra'  mi :  plural  of  ramus. 
Ra'  mus :  the  branch  of  an  organ. 
Rec'  tus :  straight. 
Rhin'  al :  pertaining  to  the  nose. 
Ro  Ian'  do  :  an  anatomist. 
Ro  tun'  dum  :  round. 

Ru'  mi  nant  (ruminare,  to  chew  the  cud)  :  any  of  the  ungulates  which 
chew  the  cud. 

Sa'  crum  (sacer,  sacred)  :  the  part  of  the  backbone  between  the  innomi- 
nate bones. 

Sag'  it  tal  (sagitta,  an  arrow)  :  a  name  given  to  a  vertical  longitu- 
dinal plane  of  the  body. 

Scaph'  oid  (skapha,  a  boat)  :  a  bone  in  the  wrist  and  also  the  ankle. 

Sciat'ic  (siat'ic)  :  relating  to  structures  in  the  region  of  the  ischium. 

Scle  rot'  ic  (skleros,  hard)  :  relating  to  the  outer  coat  of  the  eye. 

Se  ba'  ce  ous  (sebum,  suet  or  fat)  :  the  name  of  glands  in  the  skin. 

Sec  to'  ri  al  (secare,  to  cut)  :  the  carnassial  or  last  premolar  tooth  in 
many  of  the.  carnivora. 

Semilu'nar  (semi,  half;  luna,  moon). 

Ses'amoid  (sesamon,  a  grain;  oid,  like):  the  name  of  small  bones 
developed  in  tendons. 

Sig'  moid :  shaped  like  the  Greek  letter  sigma. 

Si'  nus  (sinus,  a  hollow)  :  a  cavity  or  channel. 


24°  GLOSSARY. 

So'leus  (flat). 

Sper  mat7  ic  (sperma,  seed)  :  pertaining  to  the  reproductive  fluid  called 
semen. 

Sper  ma  to  zo'  a  (sperma,  seed;  zoa,  animals)  :  plural  of  spermatozoon. 

Sper  ma  to  zo'  on :  the  male  reproductive  cell  developed  in  the  testis. 

Sphen'  old  (sphen,  wedge;  old,  like). 

Sphinc'  ter  (to  squeeze)  :  the  name  of  a  muscle  surrounding  and  capa- 
ble of  closing  an  orifice. 

Splanch'  nic :  pertaining  to  the  viscera. 

Sub :  a  common  prefix  denoting  under  or  beneath. 

Sty'loid  (stulos,  a  pillar). 

Su'  pra :  a  prefix  denoting  above. 

Sul'  ci :  plural  of  sulcus. 

Sul'  cus  (sulcus,  a  furrow)  :  a  cleft  or  furrow  in  the  brain. 

Syl'vius:  a  noted  anatomist. 

Sym'physis  (sun,  together;  phuein,  to  grow)  :  the  junction  of  bones, 
usually  in  the  median  line  of  the  body. 

Syn  ar  thro' sis  (sun,  together;  arthron,  a  joint):  a  form  of  articula- 
tion in  which  the  bones  are  immovably  united. 

Sys'  tern :  a  collection  of  organs  for  one  general  purpose. 

Tel  en  ceph'  a  Ion  (telos,  end;  encephalon,  brain):  the  cerebral  hemi- 
spheres and  corpora  striata ;  the  end  brain. 

Te'  res :  round. 

Thai' a  mus  (thalamos,  bed)  :  the  optic  thalami  form  the  chief  part  of 
the  tween  brain. 

Thy'roid  (thureos,  a  shield;  old,  like)  :  the  name  of  structures  in  the 
region  of  the  thyroid  cartilage. 

Tib'ial  (tibia,  shin)  :  pertaining  to  the  tibia  or  shin  bone. 

Tri'  ceps  (tres,  three;  caput,  head). 

Tri  cus'  pid :  having  three  points  or  cusps. 

Tri  gem'  i  nal :  the  fifth  cranial  nerve,  so  called  because  of  its  three 
divisions. 

Tro  chan'  ter :  the  name  of  two  processes  on  the  femur. 

Troch'lear  (trochilia,  a  pulley). 

Tur'  bin  al :  one  of  the  turbinated  or  lateral  ethmoid  bones. 

Tym'panum  (tumpanum,  a  drum)  :  the  middle  ear. 

Um  bil'  i  cus  (navel)  :  the  depressed  cicatrix  in  the  center  of  the 
abdomen  marking  the  hole  giving  passage  to  the  vessels  formerly 
connecting  the  young  with  the  mother. 

Un'ciform  (uncus,  a  hook;  forma,  form)  :  a  bone  of  the  carpus. 

Ungula'ta  (ungula,  a  hoof)  :  an  order  of  mammals  characterized  by 
hoofs. 

U  re'  ter :  the  tube  from  the  kidney  to  the  bladder. 


GLOSSARY.  241 

U  re'  thra :  the  tube  from  the  bladder  to  the  exterior. 

IP  ter  us :  the  womb  or  cavity  in  which  the  young  are  developed. 

Ven'  trad  {venter,  stomach)  :  toward  a  plane  passing  along  the  under- 
side. 

Ver'  te  bra  {vert ere,  to  turn)  :  a  bone  of  the  spinal  column. 
Ver'  te  brae  :  plural  of  vertebra. 
Vestig'ial:  rudimentary;  existing  only  as  a  trace. 
Vis'  ce  ra :  the  organs  within  the  body  cavity. 

Whar'  ton :  name  of  the  duct  from  the  sublingual  gland. 

Wil'  lis  :  an  anatomist. 

Wir'  sung :  an  anatomist ;  name  of  a  duct  from  the  pancreas. 

Xiph'  old  :  same  as  ensiform. 

Zy  go'  ma  (zugoma,  cheek-bone)  :  the  arch  formed  by  a  process  of  the 
temporal  bone  and  the  malar. 


INDEX. 


Air  sacs,  161 
Alimentary  canal,   116 

walls  of,  118 
Alveoli,  161 
Amphibia,  2 
Anaesthetizing,  5 
Anatomy,   I 
Antibrachium,  56 
Aorta,  132 

Appendix  vermiformis,  117,  126 
Arteries 

head  and  neck,  135 

pelvic  limb,   140 

thoracic  limb,  137 

trunk,    132 
Artiodactyla,  231 
Association  fibers,  204 
Atlas,  44 

Auditory  organ,  224 
Axis,  44 

IHle,    123 
Bile  cyst,  127 
Bone,  structure  of,  25 
Bones,  ear,  225 

head,  26 

method  of  cleaning,   n,   12 

number  of,  21 

pelvic   limb,   64 

table  of,  22 

thoracic  limb,  52 
Brachial  plexus,  208 
Brain,  175 

arteries,  136 

basal  ganglia,  186 

commissures,   183 

external  features,  176 

extraction  of,   10-12 

fibers  of,  202 

human,    228 

internal  structure,  180 

mammalian,  228 

parts  of,   176 

rabbit's,  229 

ventricles  of,  181 


weight  of  in  mammals,  229 
Bronchial   tubes,    159 

Caecum,  232 
Capillaries,  148 
Carpus,  57 
Cartilage  cells,  14 
Cerebellar  tracts,  200 
Cerebellum,  191 
Cerebrum,    177 
Chevron  bones,  48 
Chiroptera,  232 
Classification,  2 
Clavicle,  53 
Clitoris,  232 
Cloaca,  173 
Coccyx,  232 
Cochlea,  225,  226 
Ccelom,  233 
Conjunctiva,  220 
Connective  tissue,  16 
Corona  radiata,  203 
Corpora   quadrigemina,    186 

striata,  188 
Corpus  callosum,   184 
Cranium,  26 
Crossed  pyramidal  tract,   191,   197, 

199,    200,    202 

Crus,  69 

Cutaneous  sense  organs,  219 

Decussation,  motor,  200 

sensory,  203 
.Dermis,   18 
Didelphia,  233 

care  of  young,  173 
Diencephalon,  188,  233 
Digestive  system,  105 

of  mammals,   125 
Digit,  234 
Digitigrade,   62 
Dissection,  preparation  for,  5-12 

Ear,  224 

bones  containing,  30 


243 


244 


INDEX. 


Edentata,  234 

Embryology,  I 

Epithelium,    13 

Esophagus,   114 

Ethmoid,  26 

Eutheria,    234 

Eye,   220 

muscles   of,   221 
nerves  of,  205 
structure  of,  222 

Excretory   system,    164 

Fallopian   tube,    167 
Families,  3 
Fasciculus,  muscle,  77 

Goll  and  Burdach,  199 
Feces,  16 
Femur,  66 
Fiber  tracts,  199 
Fibula,  68 
Fillet,    197,  203 
Foot,  bones  of,  70 

of  horse,  57,  58 
Foramina  of  skull,  34 
Formaldehyde,  4 
Formalin,  4,  235 
Formatio  reticularis,  203 

Gall  bladder,   123 
Ganglia,  sympathetic,  214 
Genera,  3 
Gland,   105 

Cowper's,  173 

digestive,   121 

ductless,  154 

lachrymal,    221 

lymphatic,   150 

mammary,  170 

prostate,    173 

sebaceous,  164 
Glands,  120 

salivary,   121 

stomach,  118 

sudiparous,  164 
Gustatory  organ,  220 

Hair,  20 

Hand,  bones  of,  59 

Heart,   129 

Histology,  I 

Horns,  26 

Horse,  evolution  of,  62 

limbs  of,  56,  60 
Humerus,  54 


Hymen,   168 
Hyoid  bones,  40 

Inguinal   canal,    172 

Injection  method  of,  5-8 

Innominate,  64 

Internal  capsule,  189,  190,  200,  203 

Intestine,  115 

Invertebrata,  2 

Involuntary  muscle,  13 

Joints,  kinds,  74 

ligaments  of,  76 
structure  of,  75 

Kidney,   parts,    164 

structure,  165 
Kidneys  of  mammals,  174 
Knee-joint,  75 

Lachrymal  bones,  38 
Lacteals,  119,  120 
Larynx,   157 

Lateral  ground  bundle,  200 
Ligaments,  74,   125 
Liver,  120,  122 
Lumbar  plexus,  211 
Lungs,  158,  160 
Lymphatic  system,  149 
injection   of,  8,  9 
Lymph  glands,  150 

Malar  bone,  39 
Mandible,  39 
Marsupialia,  3,   173 
Maxillary  bone,  36 
Maxillo-turbinal,  37 
Mediastinum,    161 
Medulla  oblongata,  190 
Meninges,  175 

Mesencephalon,  185,  186,  237 
Mesenteries,  124 
Metacarpus,  60 
Metatarsus,  71 
Monotremata,  237 
Morphology,  I 
Motor  decussation,  201 

tract,  203 
Mouth,  107 

Mucous  membrane,  125 
Muscles,  77 

abdomen,  88 

chest,  81 

dissection  of,  79 


INDEX. 


245 


Muscles,  forelimb,  84,  90,  98 

head  and  neck,  82 

hind  limb,  94,  101,  102 

kinds,  78 

structure,  15 

trunk,  92 
Alyelencephalon,    190 

Nares,  33,  35,  157 
Nasal  bone,    158 
Nerve,  afferent,  231 

auditory,  227 

cell,  196,  198 

efferent,  234 

fibers,  relation  of,  197 

tracts,   199 
Nerves,  arm,  208 

cranial,  205 

digits,  201 

leg,  211 

motor,  206 

peripheral,  204 

plexuses  of,  207,  216 

sensory,  206 

spinal,   194,   195,  207 

sympathetic,  214 
Neurone,  198 
Nomenclature,   3 

Nuclei,  gracilis  and  cuneatus,   199 
Nucleus  caudatus,  189 

Occipital  bone,  31 
Olfactory  organ,  219 
Omenta,  124 
Optic  thalami,  188 
Orbital  cavity,  238 
Orders,   3 
Organs,  13 

of  the  body,  106 
Ornithodelphia,   169,  238 
Ova  of  mammals,  169 
Ovaries,   168 

Pacinian  corpuscle,  219 
Pain,  sense  organs  of,  219 
Palatine   bone,    37 
Pancreas,  120,  123 
Paralysis,  201 
Parietal  bone,  31 
Patella,  67 
Peduncles  of  cerebellum,  191 

cerebrum,  238 
Penis,   172 
Perissodactyla,  238 


Peritoneum,   117,  124 
Phalanges,  61,  72,  238 
Pharynx,  112 
Phylogeny,  2 

horse,  238 
Physiology,   I 
Pineal  body,  188 
Pituitary  body,  178 
Plantigrade,  62 
Pleura,  161 

Portal  system,  120,  144 
Premaxillary  bone,  36 
Preservation  of  material,  4 
Primates,  239 
Projection  fibers,  203 
Protochordata,  2 
Prototheria,  3,  239 

Quadriceps  extensor  muscle,  96 
Quadrigemina,  corpora,  186 

Radius,  55 
Reflex  action,  199 
Reproductive  system,  167 
Respiratory   system,    157 
Retina,  223 
Ribs,  50 
Ruminant,  239 

stomach  of,  126 

Sacral  plexus,  213 
Sacrum,  46 
Salivary  glands,  121 
Scapula,  52 
Sciatic  nerve,  213 
Sebaceous  glands,   19 
Sense  organs,  218 
Sensory  decussation,  203 
Sensory  tract,  203 
Serous  membrane,  125 
Sesamoid  bones,  21 
Shoulder  girdle,  53 
Skeleton,  21 
Skin,  18,  19 

sense  organs,  219 
Skull,  26 

Smell,  organ  of,  219 
Solar  plexus,  216 
Species,  3 
Spermatozoa,   172 
Sphenoid  bone,  33 
Spinal  cord,  193 
Spleen,  120,  154 
Sternum,  48 


246 


INDEX. 


Stomach,   115 
Suprarenal  bodies,  155 
Sweat  glands,  19 
Sympathetic  nervous  system,  214 
Synovial  membrane,  75 
Systems,  13 

Tarsus,  70 
Taste,  organ  of,  220 
Taxonomy,  2 
Teeth,  108 

mammalian,   in 
Telencephalon,  177,  240 
Temporal  bone,  29 
Testes,   170 

Thoracic  duct,  152,  153 
Thymus  gland,  155 
Thyroid  gland,  154 
Tibia,  68 
Tissues,  13 

Tongue,  107  , 

Tonsil,  107,  108 
Tooth,  structure,  109 
Trachea,  159,  160 
Tympanum,  240 

Ulna,  55 
Ungulata,  240 

evolution  of,  62 
Ureter,   166 
Urethra,  166 
Urogenital  system,  164 
mammalian,  173 


Uterus,  167,  241 

Vagina,  168 

Valves,  heart,  129,  132 

veins,  143 
Vascular  system,  129 

injection  of,  5-8 
Veins,    142 

lungs,    147 

trunk,  145 
Vena  cava,  145 

Vermiform  appendix,   117,   126 
Vertebrae,  41 

caudal,  47 

cervical,  45 

lumbar,  46 

number  in  mammals,  48 

plan  of,  44 

thoracic,   46 
Villi,  119 
Viscera,   113 
Vocal  cords,  160 
Vomer,   37 

Wharton's  duct,  121 
Willis,  circle  of,  136 

Xiphoid  process,  49 

Zygoma,  29 
Zygomatic   process,   28 


o 

,  I 


<3 

• 

o 


DATE    DUE    SLIP 

UNIVERSITY  OF  CALIFORNIA  MEDICAL  SCHOOL  LIBRARY 


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